On some people's accounts, when they attempt to add time to a project they may see different mentions.This functionality is quite old and will be deprecated it the near future, but let me quickly explain why this happens.
We consider "@mention" as a project alias and create it for each user-project individually. By default, it is set by project creator, but each member can further update it per his own preference.
You have started working on a new project. Its code name was "buzz" and everyone get used to it.
At some point Client decided to rename the project to something more formal, based on his policies or whatever. Say now it is "@tsp-buzz-crm".
With current implementation, the whole team could keep using the old name - "@buzz", while project manager can update the name and use it in his reports.
Yeah, sounds confusing, but at that time we found it quit a good idea :)
Again, sorry for the inconvenience. If someone need any help/assistance - let us know. We will be happy to help.