Batch Uploader and PSOUniqueFieldWithinFolders validation failure?

I’m trying to use the batch uploader (out of the box - I haven’t modified it) with a content type that has two fields that use the PSOUniqueFieldWithinFolders validation. That validation works fine when I enter content via the Content Explorer, but is consistently failing when I try to add an item with the batch uploader. I’ve confirmed that the field values ARE unique, and enabled logging, but haven’t found any clues about why the validation fails.

Does anyone out there have any insight or experience with this problem?

-Kathleen