For a start, at the inquest the CAA's chief investigator essentially got up and said the TAIC report was crap and that W & B was not a causal factor. Perhaps the CAA wanted to back this up by going out and getting hard evidence through flight testing ?
Could it also be because CAA allowed certification from the Ag category into the category used for the skydiving operation without following all the correct procedures?
I suspect they were trying to cover their backside against potential legal liability by attacking the TAIC report and getting involved in the flight testing. Who actually instigated the flight tests Weheka mentions?
I agree there was some unseemly haste with parts of the investigation and TAIC missed the mark in some areas. Examination of the control column etc would certainly be helpful though I don't think this is the root cause but maybe a subsequently contributing cause.
There is no question the aircraft was being operated outside the C of G envelope. This might be OK when things are normal but when something out of the ordinary occurs then it could well be the straw that breaks the camels back. The flight testing proves nothing in my opinion.