diff --git a/src/admin/dbmappings.php b/src/admin/dbmappings.php
index 4b57a5c..67db06a 100644
--- a/src/admin/dbmappings.php
+++ b/src/admin/dbmappings.php
@@ -161,7 +161,13 @@
 {
 	// If Columns are send using POST we use them, otherwise we try to use from the view itself, if available
 	if ( isset($_POST['Mappings']) )
+	{
 		$AllMappings = $_POST['Mappings'];
+		// Reset SUBMAPPINGS when rebuilding from POST data so that stale DB-loaded
+		// string entries (fields removed in a prior delete subop) do not remain and
+		// cause "Illegal string offset" warnings when iterated as arrays (issue #61).
+		$content['SUBMAPPINGS'] = array();
+	}
 	else if ( isset($content['SUBMAPPINGS']) )
 		$AllMappings = $content['SUBMAPPINGS'];
 
diff --git a/tests/php/Unit/DbMappingSubMappingsTest.php b/tests/php/Unit/DbMappingSubMappingsTest.php
new file mode 100644
index 0000000..047b1d4
--- /dev/null
+++ b/tests/php/Unit/DbMappingSubMappingsTest.php
@@ -0,0 +1,173 @@
+<?php
+declare(strict_types=1);
+
+namespace LogAnalyzer\Tests\Unit;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Regression tests for issue #61 – "Error remove multi lines mapping in Database Mapping".
+ *
+ * Root cause: when the edit page handles a delete-subop POST request it first
+ * re-loads the full mapping from the database (which stores each field value as
+ * a plain string), then overwrites only the keys that appear in
+ * $_POST['Mappings'].  If the user had already deleted one field in a previous
+ * request, that field is absent from $_POST['Mappings'] but is still present in
+ * $content['SUBMAPPINGS'] as a *string*.  The subsequent "Process Columns for
+ * display" loop then tries to do $myColumn['MappingCaption'] = … on a string,
+ * producing "Illegal string offset" warnings.
+ *
+ * The fix resets $content['SUBMAPPINGS'] to an empty array before rebuilding it
+ * from $_POST['Mappings'], so stale DB-loaded string entries can never linger.
+ */
+final class DbMappingSubMappingsTest extends TestCase
+{
+    // -----------------------------------------------------------------------
+    // Helpers that mirror the logic extracted from src/admin/dbmappings.php
+    // -----------------------------------------------------------------------
+
+    /**
+     * Simulate the ORIGINAL (buggy) behaviour: does NOT reset SUBMAPPINGS
+     * before building from $postMappings.
+     *
+     * @param array<string,string> $dbMappings   Mappings as loaded from DB
+     *                                            (string values, keyed by fieldId)
+     * @param list<string>         $postMappings  $_POST['Mappings'] value
+     * @return array<string,mixed> The resulting $content['SUBMAPPINGS']
+     */
+    private function buildSubMappingsBuggy(array $dbMappings, array $postMappings): array
+    {
+        // Step 1: simulate the GET op=edit handler loading DB data as strings.
+        $submappings = $dbMappings;   // values are plain strings here
+
+        // Step 2: simulate the "Additional work" block WITHOUT the fix.
+        $allMappings = $postMappings; // comes from $_POST['Mappings']
+        // (no reset of $submappings)
+        foreach ($allMappings as $colKey => $fieldName) {
+            if (!is_numeric($colKey)) {
+                $submappings[$colKey] = ['MappingFieldID' => $colKey, 'MappingDbFieldName' => $fieldName];
+            } else {
+                $submappings[$fieldName] = ['MappingFieldID' => $fieldName];
+            }
+        }
+
+        return $submappings;
+    }
+
+    /**
+     * Simulate the FIXED behaviour: resets SUBMAPPINGS before building from
+     * $postMappings so that stale DB string entries are discarded.
+     *
+     * @param array<string,string> $dbMappings
+     * @param list<string>         $postMappings
+     * @return array<string,mixed>
+     */
+    private function buildSubMappingsFixed(array $dbMappings, array $postMappings): array
+    {
+        // Step 1: simulate the GET op=edit handler loading DB data as strings.
+        $submappings = $dbMappings;
+
+        // Step 2: simulate the "Additional work" block WITH the fix.
+        $allMappings  = $postMappings;
+        $submappings  = [];           // <-- the fix: reset before rebuilding
+        foreach ($allMappings as $colKey => $fieldName) {
+            if (!is_numeric($colKey)) {
+                $submappings[$colKey] = ['MappingFieldID' => $colKey, 'MappingDbFieldName' => $fieldName];
+            } else {
+                $submappings[$fieldName] = ['MappingFieldID' => $fieldName];
+            }
+        }
+
+        return $submappings;
+    }
+
+    // -----------------------------------------------------------------------
+    // Tests
+    // -----------------------------------------------------------------------
+
+    /**
+     * After a first delete the form only sends the remaining fields.
+     * The ORIGINAL code leaves the removed field as a string in SUBMAPPINGS,
+     * which would later cause "Illegal string offset" warnings.
+     */
+    public function testBuggyCodeLeavesStaleStringEntryAfterPartialPost(): void
+    {
+        $dbMappings   = ['field1' => 'dbcol1', 'field2' => 'dbcol2', 'field3' => 'dbcol3'];
+        // Second delete: field3 was already removed in a prior request so it is
+        // absent from the form; only field1 and field2 are submitted.
+        $postMappings = ['field1', 'field2'];
+
+        $result = $this->buildSubMappingsBuggy($dbMappings, $postMappings);
+
+        // field3 is still present as a plain string – the bug.
+        self::assertArrayHasKey('field3', $result);
+        self::assertIsString($result['field3'], 'Buggy code leaves field3 as a string');
+
+        // Trying to set an array offset on that string would trigger the warning.
+        // Demonstrate the error condition without actually triggering E_WARNING.
+        self::assertFalse(is_array($result['field3']));
+    }
+
+    /**
+     * The FIXED code resets SUBMAPPINGS before rebuilding from POST, so stale
+     * DB string entries are never present in the result.
+     */
+    public function testFixedCodeContainsOnlyPostFieldsAsArrays(): void
+    {
+        $dbMappings   = ['field1' => 'dbcol1', 'field2' => 'dbcol2', 'field3' => 'dbcol3'];
+        $postMappings = ['field1', 'field2'];
+
+        $result = $this->buildSubMappingsFixed($dbMappings, $postMappings);
+
+        // field3 must be gone.
+        self::assertArrayNotHasKey('field3', $result, 'Fixed code must not retain stale DB entry for field3');
+
+        // The remaining entries must be arrays (not strings).
+        self::assertArrayHasKey('field1', $result);
+        self::assertIsArray($result['field1']);
+        self::assertArrayHasKey('field2', $result);
+        self::assertIsArray($result['field2']);
+    }
+
+    /**
+     * When all DB fields are present in the POST (e.g., the very first delete
+     * operation) both the buggy and fixed paths produce the same correct result:
+     * all entries are arrays.
+     */
+    public function testAllDbFieldsPresentInPostProducesCorrectResultBothPaths(): void
+    {
+        $dbMappings   = ['field1' => 'dbcol1', 'field2' => 'dbcol2', 'field3' => 'dbcol3'];
+        $postMappings = ['field1', 'field2', 'field3'];
+
+        $buggy = $this->buildSubMappingsBuggy($dbMappings, $postMappings);
+        $fixed = $this->buildSubMappingsFixed($dbMappings, $postMappings);
+
+        foreach (['field1', 'field2', 'field3'] as $field) {
+            self::assertIsArray($buggy[$field]);
+            self::assertIsArray($fixed[$field]);
+        }
+    }
+
+    /**
+     * Fixed code: first POST includes all fields → no stale entries.
+     * Second POST removes one field → SUBMAPPINGS still clean.
+     */
+    public function testSequentialDeletesNeverLeaveStaleEntries(): void
+    {
+        $dbMappings = ['field1' => 'dbcol1', 'field2' => 'dbcol2', 'field3' => 'dbcol3'];
+
+        // First delete: field3 removed; form still sends all three before delete.
+        $after1 = $this->buildSubMappingsFixed($dbMappings, ['field1', 'field2', 'field3']);
+        unset($after1['field3']); // simulate subop_delete
+        self::assertCount(2, $after1);
+
+        // Second delete: field2 removed; POST now only sends field1 and field2.
+        $after2 = $this->buildSubMappingsFixed($dbMappings, ['field1', 'field2']);
+        unset($after2['field2']); // simulate subop_delete
+        self::assertCount(1, $after2);
+        self::assertArrayHasKey('field1', $after2);
+        self::assertArrayNotHasKey('field2', $after2);
+        self::assertArrayNotHasKey('field3', $after2);
+        self::assertIsArray($after2['field1']);
+    }
+}