Splash window "About" ("Info" in German) can not be closed on MacOS

[xifra]

First of all, thanks a lot for your wonderful piece of software! I am trying to contribute, as good as I am able to, by submitting this bug report. I assume it is a bug, what I describe below.

When selecting menu item "About" in Quba's "Help" menu, a window opens on top of the application's main window, which gives version information etc. (see attached screenshot). This window can not be closed and also the main window can no longer be closed, and, hence, this blocks the whole application. Effectively, the whole Quba application becomes inaccessible. Shutting down the application is required to get out of this broken state.