As a user, I do not want error/warnings I cannot get rid of (however useful).
While testing NX3 SNAPSHOT I shutdown my server but forgot to close NX in my browser. I noticed NX3 has a cool warning now that tells you there is a disconnect. However, following this warning if you try and do anything you get a message popout on the screen "There is a problem communicating with server." This is similar to the NX2 message which I believe says timeout, however, the NX3 message will not go away on close (OK) - instead it reopens the popout and adds another warning window on the right side.
I don't feel this is good usability but if intentional, there's no point I see to having the OK button as is. It might as well be a close tab button.
This is not an issue in NX2, tho I do believe NX3 performance is better besides this aspect.
I believe I noticed this in the milestone build as well but wanted to check the snapshot. I did not see this in my notes however nor did I (re)recheck at this time. I can if you like and it helps.