Messages window jumping all over the place in Yosemite?

Since upgrading to Yosemite, my Messages window (specifically, the window with the message threads in them, Cmd-0) is jumping all over my screen when clicking on the window to bring it forward or clicking off the messages window into another window or to the finder. It's not 100% reproducible, but happens maybe 25-50% of the time.

I'll be working in Safari, click on the messages window to view a chat, then click in the box to type a response and the window moves to the location of the mouse, as if I had dragged it there. Or I'll type a reply to a message, and then click onto Mail or Safari, and the window magically jumps to where I clicked, again as if I had dragged the window.

I have not experienced this behavior with any other apps or windows. Only the Messages window in the Messages app, and only since upgrading to Yosemite.

Has anyone else experienced this? Any ideas?