I have what sounds to be the same problem.

When turning a sharp corner or entering a roundabout (slow down and clutch in) the rev's die and it cuts out.

Takes about 10 seconds of turning her over before it restarts.

But i have no dump valve..... no intercooler.... its a standard neough blacktop.
It doesnt happen on a straight road and im 99% sure i dont have a boost leak as it accelerates fine, no hesitation etc.

Infact the car drives perfectly all the time...... untill you for example pull up to a set of red lights, turn a tight bend at 10mph....

Im lost and its doing my head in!!!!

Any idea's???