I archived an older version of the project since it was released a while ago and no further development was going against it.
Then, I re-opened a resolved issue that had been previously set as 'Fix For' that version. I didn't visit the Fix version field on my additional info screen so I didn't notice what it said, but presumably, it wouldn't have shown the older version in the dropdown because, being archived, it won't show that version anymore.
So, after re-opening the issue, i ended up with an issue scheduled to be fixed for a very old version.
The app should warn me if re-opening an issue for an archived version.