Edit window moves on selecting clip

This is a strange one, and a little hard to describe. I use a dual-monitor setup, driving one monitor from the HDMI out on my 2011 Mac Mini Server (running 10.9.4), and the other from the Thunderbolt output.



When I'm working in the edit window spread across two displays, if I click on a clip that's anywhere near the inner boundaries of either of the two monitors, the display changes horizontal position. At first, I thought it was to make the entire clip visible on one screen, but it will also span the boundary between the two screens with the selected clip. Once I've clicked on one clip in a track, clicking on other clips in that track doesn't move the display, but if I click on another clip in another track, it does it again. It used not to do this.



I know there are a number of strange display behaviors in Mavericks - could this be one of them? It's not lethal, but it's disorienting when I'm focused on doing an edit and things start moving around. I've looked in System Prefs as well as PT prefs for a likely culprit, but I can't see anything that would make sense.



Any ideas?



Thanks,



Myles