So I've not had this problem. (I use FF on windows 10) But apparently this is an issue that vBulletin has left it hanging on it's users to figure out. (Once again they have tried to throw it on Google and other companies to be the problem. Their responses are certainly making me consider moving to xenforo.) From what I've found, many who report this problem are using Chrome. Apparently the "fix" is to hit the enter key first in the reply window, or switch to default mode. (Click the A/A button on the to left of the reply window) The other "fix" is to make a global notice at the top of the reply window to tell you how to do this. (But with how people ignore notices, I don't see that being worthwhile to do.) There's one other thing I can try in the css, but I'd like to confirm everyone having problems are using chrome. (And it's the latest update of chrome)