Definitely has all the hallmarks of the bad turbo seals, almost exactly what mine was doing prior to having it replaced.
Does the smoke have a very pungent odour, in which case it is the coolant seal, a trick I used to do to avoid the smoke screen at the lights was to sit the car at about 1250-1500 rpm when as lights etc, the additional airflow through the turbo is enough to allow the shaft & seal to seat correctly.
There are a lot of theories out there on the matter, one that seems plausible is that the aftermarket downpipe creates lower pressure on the turbine side of the shaft, while the stock intake on the compressor side has a higher pressure, the shaft naturally favours the low pressure side and moves enough to cause the coolant seal to not sit correctly.
The remedy is to fit a much more open intake, i.e CAI, or SRI with an aftermarket TIP to reduce the intake side pressure and allow the shaft to retain its balance, worth considering if you have any hassles getting the replacement item done under warranty.
Nearly all men can stand adversity. But if you want to test a man's character - give him power.
Abraham Lincoln