Global Menus not working in all scenarios



Hello there,

I've recently installed Ubuntu MATE 18.04, and I've liked it a lot so far. Only one issue I'm having, is that with some applications, the global menu will work, and with some it won't.
For instance, with both Chrome and LibreOffice it works fine, but with Caja, MATE Terminal, TuxGuitar and GIMP it won't. They were all working (apart from GIMP) when I first installed, but now, for some reason, they're not anymore.

Is there any library/dependency that I might be missing?