few other things to look at....
what air temp is the temp getting up to ? have you checked that and referenced it to your air temp ignition correction table?
Boost leak could be causing this as well, ive seen boost leaks do some weird things in the past and it IS possible for the leak to cause this.
When you have a boost leak, the turbo is working sooo much harder that the air temp would go through the roof and also cause ignition retard...
Can you send me a log of the dyno run from the datalogit ? the text file with all the values ?
post them up ?