Updated solvespace to latest git master, bug still presented.

Can you please build the platform branch from this repository and see if it helps?

I built it from platform branch, same error.
Difference is - when I close window I get ~20 similar pairs of errors:

(solvespace:27299): glibmm-CRITICAL **: 21:41:25.228: Glib::ObjectBase* Glib::wrap_create_new_wrapper(GObject*): assertion 'wrap_func_table != nullptr' failed

(solvespace:27299): glibmm-WARNING **: 21:41:25.228: Failed to wrap object of type 'GtkWindow'. Hint: this error is commonly caused by failing to call a library init() function.

That's really odd. Which GTK version?

Reinstalled gtk packages, rebooted PC, changed gnome shell and gtk themes to default (adwaita). Same.

Sorry, no idea. I have the exact same GTK version and everything works.

Bug disappeared. Close issue?

Can this issue be re-opened? I am running Ubuntu 18.04.3 LTS and I have this exact same problem. This is not specific to any one application for me, it's the entire operating system. For example, if I have mail open and another application open, if mail is not the currently-focused window and I click on any menu in the mail window (evolution mail), the menu stops working. The only way I can get the menus to again re-appear is to quit the program and re-open. Very frustrating.

What is going on: When main window is inactive, pressing main menu breaks drop-downs, they stop working.

Why are you asking to reopen a SolveSpace issue if you say that your problem isn't SolveSpace-specific?

My apologies, I wasn't aware that it was specific to SolveSpace; it is however the identical issue which, in my mind, means it is not specific to SolveSpace but is a bug within the operating system itself.
Should I open a new issue?

I should also mention that the error I get if I launch from terminal and reproduce the issue is identical:
(evolution:12656): Gdk-CRITICAL **: 10:21:32.823: Window 0x5604a7d4d4b0 has not been made visible in GdkSeatGrabPrepareFunc

You're correct; it is not an issue with SolveSpace, although before now no one has reported that it affects other applications too. Unfortunately, because it is not an issue with SolveSpace, there is nothing I can do about it, so there is no point in keeping the bug open or opening a new one.

You could report it against GTK upstream. Though, if I recall, I did mention it on GTK IRC channel and we concluded it's probably not GTK either, but rather Mesa or i965.

Ok, thanks for the help whitequark.
I've reported it in askubuntu.com here: https://askubuntu.com/questions/1201041/issue-with-menu-not-being-displayed-when-clicked-on-and-window-is-not-focused-be

So, based on your last post, you've seen this issue as well? Do you still experience this issue or were you able to correct it?

I'm investigating a similar issue and I think this is how to reproduce:

1. In GNOME settings | Region & Language, select Allow different sources for each window.
2. Use GNOME on XOrg session.
3. When window is on background, right-click the menubar.
4. Repeat a few times if needed.
5. Issue is present on Ubuntu 18.04, but no longer there on Ubuntu 20.04.

See also: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/1899