[Koha] 'mixed materials' showing up as 'book' item types

I have a number of items that are cataloged at 'mixed materials' both in the 000 field and the 008 field, but they are showing up as 'book' item types on the original search results page. If I click on the item title or item details it shows correctly as 'mixed materials.' I heard this was a bug in the old Koha version and I think these records must have carried over. The mixed material records I create in the new version display correctly. Any suggestions on how I can fix the records carried over from the old Koha version with the bug? Thanks, Heidi