Just stumbled on something unexpected, if not problematic, in the admin interface.
I was looking at the guest user page accessed via the Admin > Access > Users > guest route and I hit the save button *without* making a single edit. Interestingly, I got the following messages about the result of that save...
[tick] Change: roles
[tick] Saved Page: /processwire/access/users/guest/
[cross] The guest role is required
...which isn't exactly what I'd have expected having made no changes. I've checked with others in the chatroom and they are seeing the same thing.
This seems similar to something that I found the other day regarding PW not 'keeping' the checked status of submitted checkboxes if they have the 'disabled' attribute set. As it looks like the roles checkboxes are all disabled for the guest user that might be why it's picking up a change.