Opera Browser Problem

Opera browser cause problems... Some guys here are using it and they began to complaint about not being able to assign, close issues... For case closing operation, we do have "assing" field required, and, unless the user chooses his/her own name, he/she can not close the case (one of the cases).
Brief, it seems to be that with 3.4.1, Opera may not work well (although it was, before)