Comment 4 for bug 1724250

Another report of the same issue: https://askubuntu.com/questions/983629/terminal-window-stuck-with-the-corner-of-another-window-drawn-on-it

It's interesting that you have 4 buttons instead of 3 (and it's the same at that other report).

Did you somehow add a 4th button? What and how exactly? Or does it only appear in gnome-terminal? What do those buttons do if you click on them?