It turns out that this occurs when there happen to exist two instances with the same name. In this case, there were two filesystems called Volume1
, so Windows renamed the second to Volume1#1
. The fact that the first instance was not updated with new data was most likely a coincidence, there probably was no activity on Volume1
.
It is not clear what information is used to map the first and second volume to their corresponding instances though, it might even be random.