Thanks for the response and the pull request. In addition to what you indicated there is also a problem with accessing the first column of categories (by arrow keys) – at least on my laptop. Do you see that as well?
Clicking the power button in Budgie Menu has a log-out option. This same dialog is brought up by clicking the User Indicator applet if you add that to your panel. If you prefer a more traditional menu, this applet can be installed from the AUR, which also has a log-out option.
For this, I would ask to file a report here so it’s on the radar and the feasibility can be looked at and discussed.
EDIT: Upon quick discussion on Matrix, it sounds like this used to work, but the applet hasn’t seen any changes in a few years. So it might be a change in Mutter, in which case…
EDIT 2: There are a couple open issues on Mutter which might be related to this: