The exact opposite actually happens. You will see when wastegate opens it starts dumping too much boost. Is actually very good thing.
I have a local truck with this design dp, running low 12's on stock turbo. I had to go into the initial WG duty cycle table in chips and max them at 100%, meaning remain closed initially.
I have the MPH hack in there also BTW.
What ends up happening is WG stays shut until boost rises up, then it just slightly opens when it reaches desired boost. Once it opens just a tad, control is no problem running full open dump.
I know I mentioned this before but we picked up 6mph in quarter just with this downpipe.