I've seen it quite a few times over the years, and even reported it to Matt, for me it seems to happen if the mouse is sitting on, traverses, or is clicked on, the word "Edit" on the MC Menu Bar fairly soon after something has been manually imported into MC. Plus it can happen when MC is told not to analyse files on import.
For me it is fairly easy to reproduce as it usually happens soon after using Explorer to add or update Skins and TrackInfo Plugins where the only "playable media" is image files along with things like css, html, javascript and xml files.