Index: magnolia-core/src/main/java/info/magnolia/module/delta/AddMimeMappingTask.java
===================================================================
--- magnolia-core/src/main/java/info/magnolia/module/delta/AddMimeMappingTask.java	(revision 50228)
+++ magnolia-core/src/main/java/info/magnolia/module/delta/AddMimeMappingTask.java	(working copy)
@@ -86,6 +86,7 @@
 
         if (!mimeNode.hasContent(extension)) {
             Content m = mimeNode.createContent(extension, ItemType.CONTENTNODE);
+            m.createNodeData("extension").setValue(extension);
             m.createNodeData("mime-type").setValue(mime);
             m.createNodeData("icon").setValue(icon);
         }