When I route Layers to the Song Channel and then switch song and back to that song, the routing of the layers changed from Song channel to the out-channel of the song channel. This is reproducable.
step by step:
set Song channel to “Stereo Out”
set Layer 1 channel to Song channel
switch song
switch back to that song
Layer 1 channel shows “Stereo Out”
set Song Channel to “MAIN”
set Layer 1 to Song channel
switch song
switch back to that song
Layer 1 channel shows “MAIN”