"rotate" effect not working?

Yesterday I upgraded my kdenlive to svn-1801. I noticed some very nice improvements, at first place the fact that the clip is now resized correctly to the monitor size when pushing the _play_ button :-).

Also, there is a newly implemented effect, rotate, but I must admit, i didn't get it working. When I apply this effect to a clip on the timeline, this clip becomes black in the timeline monitor, and if I render the video, the correspondent part of it will be black as well. This happens regardless of which effect settings I choose (even with "no" settings, i.e. no actual rotation).

Did I miss something?