It is very strange indeed. One of the main resaons is because the actual (physical size) of the wastegate opening is alot bigger on these new series turbos (BB). The flapper door is bigger of course to cover up that wastegate opening on the turbine housing. It appears that it is more susceptible to being blown open because of this. We have seen this on many of the new Garrett style turbos. There are also other reasons I can add to this! Greg and I will go through this later in a different post to explain this phenomenon. This is new to us and we are like nerdy school kids trying to figure it all out.