Try this for a workaround while I delve deeper into this problem.
Click Here and then choose Full WYSIWYG Editing under Miscellaneous Options. If that doesn't work try standard or basic.
Bahh, I'm not here to complain, but this has happened some more (even today). Granted, I didn't do the suggested fixes (hence why I'm not complaining) but I'm getting this gray box in both quick reply and advanced. Annoying, but it just tempers my posting frequency.