That's the only thing I have ever seen. Did you check the jack/cable drop going back to the closet? If you plug the phone directly into the switch will it do it eventually?
I have had some strange problems with some of the higher end phones that ended up in them being RMA'ed. Screens going blank or flipping upside down, screen fading out, clicking audio....
So far the IP230 has been the most trouble free of the lot. We haven't deployed many of the IP265, but the Ip560 is the one that seems to have the most out of box failures and strange issues.