Code completion window does not disappear again (on X11)
If I hit enter to select a suggested completion, then the completed text is highlighted using a blue overlay. Unfortunately, this blue overlay never disappears again (and also does not scroll), meaning that I get random blue areas accumulating over my editor.
So far, the only way I have found to get rid of them is to restart builder. The areas also remain when switching between documents (which is likely expected).
Note that I am on an X11 session right now, which may well be related. This is happening on Fedora 28 with builder version "3.29.3-80-g2908ac4 flatpak-nightly".