First of all, I think you’re in the wrong section. This has nothing to do with TS Mobile. Furthermore, this is actually nothing new. This has happened many times before and it happened all the time several months ago.
The issue isn’t the Chat client. It’s the nice and not working presence system Matrix introduced.
That’s not a bug.
When user does close his client while he is connected to a server and still has a second pc or chat client running with same account, then last presence status stays as long it was changed at least once OR all chat connections are closed for more than 90 seconds (default value) to timeout.