Did you try to reinstall Flash?
Possibly you have done something on timeline check "show all layers as outline"
"When in doubt, reinstall." Should have thought of that myself. Thanks for the reminder.
I got the same problem as you describe, so if you have the addons FlashFirebug installed into Firefox browser, remove it, it's will solve the issue for good.
More info for the trouble : https://code.google.com/p/flashbug/issues/detail?id=34