When Spark is set to automatically join a room on startup (based on a bookmark), it uses room's username to name such tab. It should assign bookmark's name or the real name of a room in this case. When bookmark is opened manually, it assigns bookmark's name as a tab name.
This is actually about the name of room in the tab. When room was set to auto join on startup, it would show rooms ID, not the Name after such joining. But i can’t reproduce this now. I think Arthur might have accidentally fixed this