Index: kernel/content/attribute_edit.php
===================================================================
--- kernel/content/attribute_edit.php	(revision 23727)
+++ kernel/content/attribute_edit.php	(working copy)
@@ -235,6 +235,39 @@
 $requireFixup = false;
 $validatedAttributes = array();
 
+// Need to detect if post_max_size has been reached. If so, all post variables are gone....
+$postMaxSize = trim( ini_get( 'post_max_size' ) );
+$postMaxSizeBytes = $postMaxSize;
+$postMaxSizeUnit = 'b';
+// post_max_size can have values like 8M which needs to be converted to bytes
+$last = strtolower( $postMaxSize[strlen($postMaxSize)-1] );
+if ( !is_numeric( $last ) )
+    $postMaxSize = substr( $postMaxSize, 0, -1 );
+switch ( $last )
+{
+    case 'g':
+        $postMaxSizeBytes *= 1073741824; //= 1024 * 1024 * 1024
+        $postMaxSizeUnit = 'Gb';
+        break;
+    case 'm':
+        $postMaxSizeBytes *= 1048576; // = 1024 * 1024
+        $postMaxSizeUnit = 'Mb';
+        break;
+    case 'k':
+        $postMaxSizeBytes *= 1024;
+        $postMaxSizeUnit = 'Kb';
+        break;
+}
+if ( (int)$_SERVER['CONTENT_LENGTH'] > $postMaxSizeBytes &&  // This is not 100% acurrate as $_SERVER['CONTENT_LENGTH'] doesn't only count post data but also other things
+     count( $_POST ) === 0 )                                 // Therefore we also check if request got no post variables.
+{
+    $validation['attributes'][] = array( 'id' => '1',
+                                         'identified' => 'generalid',
+                                         'name' => ezi18n( 'kernel/content', 'Error' ),
+                                         'description' => ezi18n( 'kernel/content', 'The request sent to the server was too big to be accepted. This probably means that you uploaded a file which was too big. The maximum allowed request size is %max_size_string.', null, array( '%max_size_string' => "$postMaxSize $postMaxSizeUnit" ) ) );
+    $validation['processed'] = true;
+}
+
 if ( $storingAllowed && $hasObjectInput)
 {
     // Disable checking 'is_required' flag for some actions.