DB was linked to SVN repository.
I needed to move its location (apparently not supported).
So I unlinked, planning to re-link in new location, disregarding history.
Once unlinked, the source control tab UI was messed up.
Close the tab, re-open, still messed up.
Disconnect the DB, reconnect, show the source control tab, still messed up.
Close SQL Management studio, restart, show DB, show source control tab, then finally it was OK again.

Messed up = I could not see the any of the text on the setup tab that normally says "not linked... Link DB to source control..."
In its place, it was all white.