FWIW, I am booting from MMC and I get the same problem intermittantly after an alarm goes off that causes the screen to wake up (ie: Korganizer)- it doesn't happen every single time though. I've also had the same issue after using mPlayer on a few occasions.

I've been unable to narrow down the exact culprit for this behavior and seeing your guy's posts makes me think that it's more a bug in whatever application or script that is responsible for the autodimming. Also - I don't use rtcomm at all.