If player try to break safe with any tool or hand it will render breaking animation for other players around (but not for him) for 1 time and then nothing. Method breakBlock will not be called, but hardness returning a positive number. IC2 Vajra can break it, but no any other tool we tried.
No bug with 3.3.6 version.
MC: 1.7.10
Mod: latest from github

I would advise to try it once more if you have not already. If the bug exists at this point in time I can take another look at it, but I believe I've taken care of most of the ownership bugs.