"This attribute type is only used for grouping, please select a subtype" when editing works

This text shows up when I try to edit a work. It went away for a while but suddenly reappeared! All I have to do to trigger it is click the "Edit" tab on a work's page in the regular server. It disables the drop-down menus at the top of the page, locks up the work attribute selection bar and blocks any edits from going through.
I know this is suspicious because there are no grouping types in the work attributes menu. Did someone leave a scrap of code behind or is there something else going on?