WP Document Revision's post_type ('document') seems to be showing up in wp_query as an array. This is causing some trouble with a couple of other plugins which expect it to be a string. Is it your plugin which sets it as an array? Is there a good reason for it to be an array? I see that it's in the WordPress Codex spec that arrays are acceptable, and I've contacted the other plugin devs to see if they can change their code. But I'm wondering if for compatibility's sake it would be simple to just make it a string.