Unable to remove missing files

I set up an Entityqueue for a slideshow using file entities. I uploaded a few individually, but then switched to admin/content/file/import to pull in all the files at once. I deleted the files I'd originally uploaded so there wouldn't be duplicates. Once all the files had been uploaded I edited the queue and it showed that the original files were missing. When I try to remove them the "Add item" field highlights as if it's a required field and the remove button has no effect.