I'm having an issue with categories being changed after switching back and forth from a user. It's been troublesome to re-create it, so I'll best describe the situation when it happens.
I have a custom role, whose posts are generated when the user is created with that role (members on an organization's website, I'm using the Members plugin for managing the custom role). The posts are assigned a non-default category ("member posts"). I've been using User Switching to go back and forth while testing the capabilities of the new custom role.
Sometimes when I switch back to my admin user from one of these members, the post I had been looking at (not even saving or updating) will have been removed from the Member Posts category and assigned the default category. I think I notice this after I've gotten the "careful, <user> is editing this post" message on switching back. Attempting to fix it from the Quick Edit will give me "Saving disabled because <user> is editing this post". If I log out and back in with my admin account, I can change the category back, and all is fine again.
Sorry I don't have better steps to re-create it, but does this ring a bell, or happen to anyone else?