Thanks, @LlGC-jop. I'm not sure if this exactly addresses the original ticket, but I'm also not sure if there is any entirely satisfactory solution to this problem, so the question is whether this is an improvement worth merging. I'd be interested in @Saira-A's opinion as the original ticket opener.

My feeling is that this is a bit of an improvement, as it reduces some of the weirder-looking displays... but it's not perfect, as it still can result in things like this:

There's also the problem that if you open both panels, resize the window, and hit the mobile footer panel toggle buttons, then both panels seem to close unexpectedly.

However, I think for the common use case of changing the orientation of a tablet, this is probably good enough. Some of the more exotic use cases may be too complicated to fix (or the cost of a fix may exceed the benefit by making code more confusing).

Thoughts?

Thanks for the update, @LlGC-jop. I've changed the base of this PR so it goes into release 4.2.0 as planned, and I'm approving since I do not object to merging it. However, I'll leave it open until others have time to comment.