Undo not working on linux

Hi there,
I’ve noticed some strange behaviour using BB on Firefox 78.3.0 esr on Debian Buster.
When changing background colours the ctrl + z doesn’t undo the changes no matter how many times I hit it. I can use ‘History’ to undo, after which ctrl + z and shift + ctrl + z work to undo and redo respectively. I’ve tried this in on Chromium (Version 83.0.4103.116 (Developer Build)), with exactly the same results.

Strangely, using the keyboard shortucut to undo column/row/module deletion works as expected.

Any ideas how this can be fixed?