Vocal memos synchronization

Hi, I'm on iTunes 11.0.2 - OS X 10.8.3 - iOS 6.1.2 (iPhone5).

When I record a vocal memo on the iPhone and sync my iPhone with iTunes, the vocal memo is correctly synchronized on the Mac.

If I delete the memo on iTunes a message informs me that the memo will be deleted also on the iPhone, but this does not happen: the memo is still on the iPhone and it will no longer be synchronized with iTunes in the next synchronizations..

If instead I delete on the iPhone a memo previosly syncronized with the Mac, it will still remain on the Mac and it will non longer synchronized with the phone..

Any suggestions?