Bah, that's a bug of the stupid QTextBrowser control. The control allows you to output HTML to it (that's what the definitions window is), but it's really flaky on alignment. I had to mess around with it a lot to get the buttons to hover on the right like that, and it must not be happy. I'll try putting things into a table for layout and see if it's any better.
All the code plugin-side is correct. Sigh. Qt.
All the code plugin-side is correct. Sigh. Qt.