Yesterday (well 2 nights ago but less then 48h) I had an issue with some one exploiting a bug.
They:
1) joined guild (with a friend/smurf account to re-invite)
2) took all they could from guild vault
3) ./gquit
4) see step 1
I have screen shots of this player practically admitting to what he did to me via whispers, and the guild log showing him /join and /gquit-ing. Unfortunately I did not screenshot the bank before/after, they took everything from the 2 bank tabs that the lowest level guild members had access to take any items out of.
if his rank had full gbank access i don't see why that would be reportable. that's the guild leader's simpleness for giving newbies full access. if he didn't full access than report him with valid proof.