One idiosyncrasy of the DP machines is that the pre setting comes before the post setting. This means you go from off, through pre to get to post. Depending on what you are doing, you can suddenly have a very loud signal happen as it goes through the pre setting. The other thing is that many people mistakenly go from off to the first setting which is pre-fader and then run into trouble, as you well know. I really wish they would address that in a firmware update that would go from off, to post, and then to pre.
Glad it was something simple!