I was using TeXworks 0.6.2 to edit LaTeX files under Ubuntu Linux 18.04 (using Gnome with X11). Suddenly, a file that I had edited before would always open in a strange way. The preview window with the PDF would open normally. But the editor opened maximized without a titlebar, window border etc. So there was no way to minimize the editor window.

I tried to minimize the window using keyboard commands and the Window-Menu of the TeXworks editor. I managed to move the window to a different screen using keyboard commands, but still maximized without a titlebar. The window menu also did not work. Restarting TeXworks also did not help. Other files would open normally.

What finally helped: File / Remove Aux Files…
Afterwards, restart TeXworks.

I did not know that TexWorks stores window status information in aux-files. But it seems it does, as deleting these files solved the problem.

If this tip saved your day, please drop a comment. This motivates me to keep writing these kind of posts.