That's not the solution for the problem I'm having:
Turn crossfade on
Create playlist
Add random songs to playlist
Start playing a song in the playlist with all boxes UNCHECKED
As the song plays CHECK a song underneath
iTunes will not crossfade to the song checked underneath
iTunes will crossfade songs if you check them BEFORE starting the songs
iTunes did not have this issue before version 11.
Before version 11 if you changed your mind or wanted to pop in a last minute song to crossfade to it would work perfectly.