I haven't had problems since I:
(1) deleted my tree in FTM 2012,
(2) uninstalled FTM - and cleared ALL trace from my computer by going through the registry and clearing that too,
(3) restarted my computer,
(4) reinstalled FTM2012,
(5) downloaded my tree from Ancestry into FTM2012, and finally but most importantly,
(5) only use Internet Explorer (and not my preferred Chrome) when working on the tree AND only do manual syncs.
Although the above process was tedious and annoying, I've had no problems for a few weeks - and I work on the tree every day.
I might add that I've not even had problems with syncing changes to Ancestry and FTM2012 at the same time.