There are only two time when I have personally encountered this problem:
1. poor connection leading to pocket loss leading to different fight state on server end and my end (do note, however, fast connection doesn't mean good connection, there are other factors)
2. When the game is not in proper focus (you tab away/minimize etc while queuing) some OS/browser will attempt to save power by not laboring on the very power intensive flash (btw, this game is not very well optimized...), and as a result, your game state lags behind because your computer doesn't handle it.

I have yet to have any case of connection error where I am certain that my connection is good and did not perform any action to jeopardize it. I have, however, had client/browser crash on me due to memory/resource leak. But that's another issue altogether.