Call to undefined function taxonomy_menu_trails_overview_form_submit()

I just installed and enabled field_group module, created a fieldgroup on a content type, and now any time I submit its Manage Fields form I get a WSOD with the error "Call to undefined function taxonomy_menu_trails_overview_form_submit()". Not sure if this is caused by taxonomy_menu_trails or field_group so I flipped a coin and posted the issue to taxonomy_menu_trails.