Confirmed this behavior in 18.05 and 18.11. To test: - Create an itype with a comma in its description - Create items without an itype - Put those items into item batch modification - Attempt to set items to your new itype - Koha will return "No items were modified" and the itype will remain null This only occurs when items have a null itype. Batch mod can correctly set an item to an itype with a comma in the description if that item is starting from a non-null itype. This only occurs in batch modification. Item creation and single item edits work correctly with itypes with a comma in the description.
Can't replicate the error in current development version.