We have an iMac with two users A and B who
- are both logged in
- are both administrators
- have different Apple IDs (and are both logged in to their's)
Today A wanted to update an app using the Updates function in the app Store and was asked for B's password. As usual, the Apple ID was not to change, it just asked for the password. It was definitely A who first installed this app because B never uses it. In fact, it is not even on the list of "purchases" of B (it's a free app, though).
What to do about it?
Curious Addendum: A got B to log in and update the app, which worked fine without even asking for B's password or asking to close the app which was running in A's logged in account. Usually, when A updated the app in the past, it would refuse to run an update while the app was running.