Index: wp-admin/includes/image.php
===================================================================
--- wp-admin/includes/image.php	(revision 5807)
+++ wp-admin/includes/image.php	(working copy)
@@ -88,11 +88,16 @@
 			elseif ( $type[2] == 3 ) {
 				if (!imagepng( $thumbnail, $thumbpath ) ) {
 					$error = __( "Thumbnail path invalid" );
-				}
+ 				}
+ 			}
+			if( empty($error) ){
+				// Set correct file permissions
+				$stat = stat( dirname( $thumbpath ));
+				$perms = $stat['mode'] & 0000666; //same permissions as parent folder, strip off the executable bitss
+				@ chmod( $thumbpath, $perms );
 			}
-
-		}
-	} else {
+ 		}
+ 	} else {
 		$error = __( 'File not found' );
 	}