With Boost and using the plain text editor (user -> prefs -> editor prefs = Plain text area), there are a number of problems with the visualization:
1) The format select menú takes up the whole width of the area.
2) The textarea is not responsive at all and falls behind the side blocks column (or out from the page) easily.
Haven't verified if this is new issue since 3.5 (Boost+) or earlier. In the other side, with clean, the menu (1) is shown with correct width, but the text area continues being, somehow, fixed.