It happens when a tab is first opened, but before the internals are loaded (things like download buttons and such).
This just happened to be again, when I uploaded some host files to a test hub.
probably reproduction steps:
So, make a new hub.
Upload a set of files to it.
Download it from the website.
Tab appears in the pager, with a / appended to the name.
This last time it stuck around a while. So, I re-started the pager, it appeared for a second before fully initializing the tab.
