Error on merging duplicate contacts, wordpress, civi 4.4.14
While it doesn't seem like it, your problem here is very similar to this.  You should check out the advice here and here; notices shouldn't be displayed in a production environment.

As for squelching those notices to begin with - I would see if the problem exists in CiviCRM 4.6 by trying the demo server.  If not, I'd say it's fine to just suppress notices using the info in the links above.