Content Organizer enabled, Drop Off Library has a bunch of custom content types as well as the default "Document" content type (library default is set to "Document").
Multiple users are allowed to upload docs, but are instructed to leave the default Document content type (with no rules attached), so that a "librarian" user can come through, edit the docs, change to the correct content type, fill out the metadata, and have the docs routed where they need to go.
Users discover that if they drag and drop multiple files, all the files remain checked out to the uploader, so the librarian can't see them and make the necessary changes. So, they ask me to set it up so files are automatically checked in.
Item Added event receiver, check in files, Bob's your uncle.
But now (and I tried to warn them of this), if someone tries to add a single file using the "new document" link or one of the Ribbon buttons, of course the usual SharePoint behavior kicks in and they are presented with the Edit form to fill out metadata, and even if they don't do anything, once they hit save, the event receiver has fired and checked in the file, and they are presented with an error message saying they can't make changes because the file is not checked out to them.
So.... is there any way I can tell from my event receiver code if the upload method was drag and drop, so that I can only auto-check-in docs that were dropped in, and leave the other ones so that the regular SharePoint Edit form will work correctly?