Weird problem with Sun keyboard and MATE 1.24

I encountered a very weird problem with MATE 1.24 that was definitely not there in earlier versions, for example 1.16. I am seeing this on Ubuntu 20.04.1 LTS and also on another Linux distribution.
I am using an old Sun USB keyboard 6 that has special keys to the left of the standard part of the keyboard. MATE had the information about this keyboard and can show a drawing of the keyboard from Keyboard Preferences->Layouts->Show.
However, with Mate 1.24, for two keys the proper label is not shown. These keys are Front (SunFront, keycode 140) and Props (SunProps, keycode 138) and instead of the proper label it shows 0x1000. This also affect shortcuts. If I try to use the SunFront key for a shortcut, the Keyboard Shortcuts menu display 0xffffff instead of SunFront
and it does not work.
(It is possible to work around the problem by mapping the SunFront keycode to a diffent keysym and make that keysym the shortcut. However, this all worked properly with MATE 1.16 so the workaround should not be necessary. I note that I have the MATE 1.16 installed on and older Linux distribution on the same machine with the same keyboard and that still works correctly).