Been looking at a k03 GTi yesterday that had one of these fitted.
On checking the fitment I noticed that the top cannister was touching a hard bit of plastic that was attached to the intake manifold via a rubber tube (vacuum related me thinks).
Could you twintake owners of either k03 or k04 cars please check to see that you have clearance between these two items as I think this could be just a fitment issue.
And in case your lost as to where to look, I've circled the area on one of RR's review pics