how to stop the Blue LED from flashing?

[crazyklaus]

I'm running the stable build on a 50D and it's really nice.
HOWEVER after the camera sits idle for 30s, the blue LED starts flashing in a 5s pattern. This is very disturbing when doing astrophotography or generally with fully dark adapted eyes.

What is this meant to indicate?
Is this caused by some setting that I have enabled?
Can this be stopped with some setting?

If not, is there a build that doesn't do it?