This site has been exhibiting this problem for me in Chrome for almost a month now. It only happens when I quote someone into the Quick Reply box.
My fix is quote them, then copy the quote, cancel the reply, then scroll down to the regular reply box, paste the quote, and reply as usual underneath.
Not sure if it's relevant or will help any, but this just happened in a reply to a private message also.
On a related note and to add to this without starting a new thread; when you're in the middle of writing a reply and decide to add a quote from someone else, if you middle click "Reply With Quote" under the new post hoping to copy and paste from a new tab, it won't actually open the new tab, instead it will start quoting that person within the same window and totally destroy all you've written so far with no way to get the text back and you have to start over.
+1, I have this issue for like 2 weeks at least now.
Reckoning Bomb - Unleashes the Reckoning upon the Scourge, inflicting ridiculous amounts of damage. Some might even say the damage is ludicrous.
vBulletin has decided not to fix it. I don't experience the bug myself and as far as I know the majority of Chrome users aren't experiencing it either (or at least haven't complained about it). It is still on the list of things to look at eventually.
Update: I still have the problem.
Real update: Accidentally typing BEFORE the QUOTE box, for some strange reason, made me able to use the spacebar... but typing afterwards made me unable.
And any reason why vBulletin doesn't feel they should fix the problem, @chaud? That seems really crappy of them...
VB4 is older software and the editor is a mess, they don't want to spend the time on it.