I had a similar thing with my Astra GSi (the car before the XFire) I had the ECU chipped, and when the car went in for Warranty work, they updated the ECU with the latest vauxhall information. This overwrote the 'custom' update I had, and put the car back to standard ECU settings.

Luckily the company that did my custom update resent it to me again free of charge.

I am not saying this is the same as DC, but potentially it could be I suppose !