Weirdly, if I switch themes to “less is more” the buttons work but they overlay the subject line:
They lay over the message itself as I scroll down, but continue to work.
Here’s a better example of the buttons on top of the message.
Tried switching between themes and in Ubuntu (the theme) the buttons don’t show any icons and there’s no information when I hover:
Taiga is the theme I was using. Darkside and Dark work like Taiga: Buttons are visible but they don’t do anything and there’s no text when I hover over the buttons. If I switch over to the vertical preview pane, that works.