I have had the same issue in IE and Chrome. I usually have to reset the IIS Worker Process on the K2 Server. The IIS Worker Process will sometimes use large amounts of memory and will need to be restarted. I have noticed it usually does this after the server runs for a month or so without being restarted. I have also noticed that if K2 runs for a long period of time without being rebooted the forms will start rendering the views in a distorted fashion. The search and filter bars do not display right and the form does not behave as designed. For instance approvers cannot approve or reject forms etc. It is annoying and maybe K2 will fix this issue in the future by creating a timer that recycles Blackpearl Server or maybe just recycles the IIS Worker Process when it reaches a certain memory. Of course we can do this on our own with windows timers but we shouldn't have to do this just to make K2 stable.
Thanks,
Bryan Peters