A longer time ago I reported (http://yabb.jriver.com/interact/index.php?topic=42336.0) this with MC12 and it got fixed, but only partially. The list of playlists is shown completely in AW since the bugfix in MC12 (and so there is no real need for me to use the right click menu), but it's still not complete for the "send to" menu:
(http://www.pix01.com/gallery/BD01FC74-5847-4306-A29B-3AA1BF99BB82/MC_Screenshot_XV/324185791_orig0.jpg)
I think it is connected to the number of playlists. Looks as MC is able to handle "only" round about 600 Playlists within the rightclick menu. As it looks in the picture above, after a number of playlists MC cuts of the list. The borderline is somewhere in the group "Alben". The list of playlists isn't complete in there.