diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index 13273532..7180c0d3 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -10190,6 +10190,14 @@ private function namePriceRowBlockFromElement(DOMElement $element, array &$fallb
             return null;
         }
 
+        // core/columns is a flex layout; WordPress rejects it with is-layout-grid.
+        // Decline when the resolved layout is grid so the container demotes to
+        // core/group, where grid layout is native.
+        $layout = $this->presentationAttributes($element)['layout'] ?? null;
+        if ( is_array($layout) && 'grid' === (string) ($layout['type'] ?? '') ) {
+            return null;
+        }
+
         $rowFallbacks = array();
         $columns = array();
         foreach ( $children as $child ) {
diff --git a/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php b/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
index 6c0f3ac7..7c120311 100644
--- a/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
+++ b/php-transformer/src/HtmlToBlocks/Patterns/ColumnsPattern.php
@@ -51,6 +51,17 @@ public function match(
             return null;
         }
 
+        // core/columns is a flex layout; WordPress rejects it with is-layout-grid.
+        // The layout resolver stamps layout:{type:grid} from signals this
+        // recognizer's style-based grid bail cannot see (grid-ish class names,
+        // class-resolved display:grid), so a would-be columns container whose
+        // layout resolves to grid must decline here and demote to core/group,
+        // where grid layout is native.
+        $layout = ( $presentationAttributes($element) )['layout'] ?? null;
+        if ( is_array($layout) && 'grid' === (string) ($layout['type'] ?? '') ) {
+            return null;
+        }
+
         $elementChildren = array();
         foreach ( $element->childNodes as $child ) {
             if ( XML_TEXT_NODE === $child->nodeType && '' === trim($child->textContent ?? '') ) {
diff --git a/php-transformer/tests/fixtures/parity/html-split-layout-grid-class-demotes-to-group.json b/php-transformer/tests/fixtures/parity/html-split-layout-grid-class-demotes-to-group.json
new file mode 100644
index 00000000..694c3c27
--- /dev/null
+++ b/php-transformer/tests/fixtures/parity/html-split-layout-grid-class-demotes-to-group.json
@@ -0,0 +1,32 @@
+{
+  "schema": "blocks-engine/php-transformer/parity-fixture/v1",
+  "name": "html-split-layout-grid-class-demotes-to-group",
+  "description": "A two-child container whose class name trips both the split-layout columns heuristic (hero-grid) and the explicit grid class signal must become a core/group with grid layout, never core/columns. core/columns is a flex layout: pairing it with layout:{type:grid} serializes the wp-block-columns + is-layout-grid combo WordPress rejects.",
+  "source_reference": {
+    "repo": "php-transformer",
+    "path": "tests/fixtures/parity/html-split-layout-grid-class-demotes-to-group.json",
+    "notes": "Derived from a bakery hero where .hero-grid { display:grid } held exactly two panes (copy + plate figure); the split-layout heuristic claimed it as columns while the grid class name stamped is-layout-grid, producing an invalid block."
+  },
+  "legacy_comparison": {
+    "skip": true,
+    "reason": "This upstream primitive fixture has no downstream legacy comparison."
+  },
+  "operation": "html_transformer.transform",
+  "input": {
+    "content": "<div class=\"hero-grid\"><div class=\"hero-text\"><h1>Fresh Bread Daily</h1><p>Baked every morning.</p></div><figure class=\"hero-plate\"><img src=\"https://example.com/bread.jpg\" alt=\"Bread\"/></figure></div>"
+  },
+  "expected_blocks": [
+    { "path": "blocks.0", "name": "core/group", "attrs": { "className": "hero-grid", "layout": { "type": "grid" } } }
+  ],
+  "expected_fallbacks": [],
+  "expect": [
+    { "path": "status", "assert": "equals", "value": "success" },
+    { "path": "fallbacks", "assert": "count", "count": 0 },
+    { "path": "blocks", "assert": "count", "count": 1 },
+    { "path": "blocks.0.innerBlocks", "assert": "count", "count": 2 },
+    { "path": "serialized_blocks", "assert": "contains", "value": "<div class=\"wp-block-group is-layout-grid wp-block-group-is-layout-grid hero-grid\">" },
+    { "path": "serialized_blocks", "assert": "contains", "value": "<!-- wp:heading {\"content\":\"Fresh Bread Daily\",\"level\":1} -->" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "wp:columns" },
+    { "path": "serialized_blocks", "assert": "not_contains", "value": "wp-block-columns" }
+  ]
+}