Aastra 57i lockups?

Anyone else out there having issues with the Aastra 57i’s locking up? We have a 57i & a 57iCT each with a 560M sidecar. We are using asterisk 1.2, and using the BLF on the sidecars. The phones seem to lockup hard every so often. I cannot find a rhyme or reason about the lock ups.