That's what I originally thought.. I installed this shield though as you can see in this thread..
http://www.zilvia.net/f/showthread.php?t=93903
And I made it all the way from San Jose to Berkeley without a problem.
When I drive "spirited-ly" they'll lock. I'll have to pull over, remove the vacuum line to the booster, and then they'll losen again.
This makes me think it isn't heat related..
I dunno man.
If replacing the MC and booster doesn't fix this.. it's going to the shop.
And if they can't fix it.... I don't even want to think about it.