Sounds like an over boost valve kicking in. Standard boost will be less than 0.95 bar and I would imagine an overboost valve kicks in at 1 bar. Just sounds like its coming in a little earlier is all. There is some gadgetry that eliminates the over boost valve, I think its called a fuel cut defender????

Anyhowz, thats my pearl of wisdom from my non existent knowledge of cossies lol.