Keep following your diagram, it's probable that the power output from the brake switch splits off to the CHMSL along with off to the turn signal switch and hazard switch. So it seems like something's getting it at this point somewhere.
Just for grins, take your bulbs out, make sure they're the correct part number, they're in correctly, and there's no foreign objects or messed up connections in the sockets. You can get a "side feed" from the parking light circuit or elsewhere if the two pins (or elements) are shorted together in one of these bulbs.
Then you can pursue it from there!