You’re referring to calling functionality specifically, not the entire app, correct?
If yes I believe this is working as designed: when another client instance is registered the app will prompt to confirm the user wants to switch before bumping the other app. There is undoubtably a background retry timer though, so once the other app unregisters on its own (i.e., that machine went to sleep) there isn’t a conflict and it can just register. From a feature request standpoint you have two options: 1) the ability to disable phone services on a given install; or, 2) eliminate the constraint of a single registration per app type (desktop, smartphone, tablet).
