Menu items visible in Unity, but not Gnome

[Jeffrey Ratcliffe <jffry posteo net>]

gscan2pdf users are reporting[1] that they cannot see menu items in
Gnome, but if they switch to, say Unity, then things work properly.

I assume that if this were a general problem with gtk+-3, then there
would be lots of bug reports, but my internet search drew a blank.

I'm wondering if it is a theme problem - gscan2pdf doesn't ship any css
and relies on defaults, as this has always worked for me (xfce and kde).

Does anyone have any insight what might be going on?

Regards

Jeff

[1] https://sourceforge.net/p/gscan2pdf/mailman/message/36394393/