DAMP duplicates mediaItem on Save


I have a "Video" MediaType that stores the URL for a Vimeo/YouTube video and a coverImage, selected with a DAMP picker.

On a DocumentType I have a DAMP picker that's configured to allow standard "Image" and the above "Video" media types.

When I select a Video in the picker and hit Save, the picker displays two items - the Video item and the coverImage selected in that Video item. In the Umbraco.config it's stored as expected, e.g. a DAMP picker with a mediaItem that has a DAMP picker itself.

If I hit Save once more, the picker now displays three items: The Video item and two copies of the coverImage - in the Umbraco.config it's now stored as a DAMP picker with two mediaItems; the Video mediaItem with it's own DAMP picker inside, and another mediaItem - as if the coverImage had been selected as the second item.

(Umbraco version: 6.1.5, DAMP version: 2.6)