I kinda have this problem also but mine is mainly when I use the "bypass".

Listening to 2ch stereo CD and hit bypass and the volume jumps a good 10db.
Scared the heck outa me the first time.

I would assume it's caused by the output of the CD player being a bit higher voltage then when everything runs through the "digital path" circuits.

It's not really a big deal as I won't be using bypass very much.