Index: src/main/java/org/apache/jackrabbit/jcr2spi/NodeImpl.java
===================================================================
--- src/main/java/org/apache/jackrabbit/jcr2spi/NodeImpl.java	(revision 605155)
+++ src/main/java/org/apache/jackrabbit/jcr2spi/NodeImpl.java	(working copy)
@@ -1436,10 +1436,10 @@
             log.error(mixin.getName() + ": not a mixin node type");
             return false;
         }
+
         NodeTypeImpl primaryType = ntMgr.getNodeType(primaryTypeName);
         if (primaryType.isNodeType(mixinName)) {
-            log.debug(mixin.getName() + ": already contained in primary node type");
-            return false;
+            return true;
         }
 
         // get list of existing nodetypes
@@ -1449,8 +1449,7 @@
 
         // check if adding new mixin conflicts with existing nodetypes
         if (entExisting.includesNodeType(mixinName)) {
-            log.debug(mixin.getName() + ": already contained in mixin types");
-            return false;
+            return true;
         }
 
         // second, build new effective node type for nts including the new mixin