After you trade, you can't use any items or spells, and I don't think you can use prayers. Probably nothing in any of the tabs. This can be fixed by banking though, but it's annoying.
Was just about to report, that why I was in here. Well don't have to now. :)
We are aware. It is a serious bug and we have every intention to fix it as soon as possible. Just be careful until then.
Yes,Please fix that bug we can't pk with this bug in the game. :[