I had to run an import where I only chose Post History to fix that table. The rest was done already. I double checked only that was selected.
It actually imported 6 things!
User groups 11 (0 seconds)
Forums 20 (0 seconds)
Thread prefixes 43 (0 seconds)
Threads 59,135 (8.88 minutes)
Posts 433,812 (4 hours, 47 minutes)
Edit history 96,916 (26.65 minutes)
So prefixes were imported again even though not selected, as well as the rest of that list.