Strange but facing same problem sometimes (not all time). I am also using Google Chrome. Thought that problem at my side only. Anyway as for now what i do is whenever this problem occur, just click on any smilies (right side of body) so it allow me to fill out the body (remove smiley later) . DON.
Yeah, apparently there's some issues with the vBulletin editor with Chrome and the vBulletin guys are working on it. My guess is it will be supported better in vBulletin 4.0 since that's pretty close.
I had it too before the upgrade. Remove the WYSIWYG editor from your Options, and use the basic one, or switch browsers.
That is just because Ctrl+B belongs to shortcut for (always show bookmark bar) in google chrome browser. DON.