This problem happened with WP2.7, probably because of the new layout. I'm pretty certain 2.6 didn't have that issue.
I uploaded a couple of screen captures so you can see what I mean in my Photobucket account:
As you can see, the Multi-page toolkit icons stretch the visual editor area to the right, instead of wrapping to the second icon row. In a 1024x768 screen, a portion of the visual editor, and one of the Multi-page toolkit icons, are partly concealed beneath the Publish panel. At higher resolutions that is no problem, of course, as you can see in the second image.
I deactivated the Viper's Video Quicktags plugin, just in case its icons were somehow the culprit, but the problem remained.
Thanks for reading.