To recreate: 1. Without having custom authorized values for bsort1/bsort2 create of edit some patrons with sort1 and sort2 values in their borrower information. 2. sort1/sort2 are free text fields 3. Create a new bsort1 and bsort2 authorized values. 4. Go back to the patron record and notice the free text field is now a dropdown with the newly create authorized values. 5. Save the patron record without changing anything. 6. The initial values for sort1/sort2 are now empty.
The same is somewhat true of the ASORT values for acquisitions, though with the added wrinkle that those authorised values aren't automatically linked to a field like the BSORT ones.