"Reply Message" Graphic gets "stuck" on

I've noticed lately that, for no apparent reason, the "Reply Message" box that comes up when you hover over the "@" button in tweets comes up and gets "stuck" in place.

Note that my mouse does NOT have to be in the Twitbin pane -- it can be on the other side of the screen. The box just pops up and won't go away until I close and re-open the sidebar.

Closing and re-opening the sidebar does get rid of the box, but it's a pain, as it obscures my peeps' tweets!

Here's a pic of the sidebar so you can see what's going on: