Quoted from smassa:
Every time I've put up a new high score song jackpot that I made from the cannon with the multiplier running it gave me the correct score.
maybe that's it then. But what's weird is I don't remember collecting another song jackpot larger than the default song bonus champion during that game, so I don't understand then why I would still be song champion if I never collected one from the cannon. Probably I just forgot that I collected one from the cannon and you are right (I don't think it was exactly a fourth of the one I collected so I'll hold off calling it a bug until I can replicate it).
Anyway, the good news is that stacking superlanes with 2x is pretty easy for 4x tour and album song bonuses -- just leave the right hand TNT target/standup as the only one needed to complete the three-bank during album MB and hit the bell with the cannon during the start of multiball and with ball saver going (with the right song going, TNT in this case) to get 2x. Then backhand ramp and do a return-lane stop after it goes over the toggled 2x return lane switch. It's actually not timed (but the 2x/3x playfield multiplier is of course) so you have can have the ball trapped as long as you need. Superlanes is by far the most valuable super-mode.