Can you please structure the html of all Composer buttons in the same way?
The Options BUTTON is the only one inside an additional DIV, which makes it much more difficult to style.
You can see the problem in Meta with Material Design Theme. Look at the last button.
Removing the div would be a bit complicated because that button/dropdown is structured like most of our other dropdowns.
I could only reproduce it at certain zoom levels, but I pushed a fix that should help. Just so I can double check: which browser/OS were you seeing this in?