It happens because doc-view was added to mailcap-mime-data; I am using
(defun ensc/mailcap-mime-data-filter (filter) "" (mapcar (lambda(major) (append (list (car major)) (remove nil (mapcar (lambda(minor) (when (funcall filter (car major) (car minor) (cdr minor)) minor)) (cdr major))))) mailcap-mime-data)) (defun ensc/no-pdf-doc-view-filter (major minor spec) (if (and (string= major "application") (string= minor "pdf") (member '(viewer . doc-view-mode) spec)) nil t)) (eval-after-load 'mailcap '(progn (setq mailcap-mime-data (ensc/mailcap-mime-data-filter 'ensc/no-pdf-doc-view-filter))))
to remove corresponding entry.
This does not solve only the org-mode problem but allows e.g. to display PDFs in gnus using an external viewer.
