My T5 might have a similar problem. I don't recall having to double-pump, but I get a little initial brake response at the top of the pedal travel, but then that seems to fade away and I have to press the pedal much further to get any significant braking. I also had the dealer flush the lines, and the situation may have improved slightly, but it may also have been my imagination. They told me that there was some recirculation (leakage) within the ABS brake pump, and that this was a problem that had been reported by a handful of owners. I've never lost fluid... this is an internal leak. Following replacement of the bad ABS pump, the other owners have apparently been happy. They told me this problem does not affect the performance of the pump when ABS is engaged... though I can't see how this is possible. My opinion is that if the pump has bad seals, it doesn't work as it was designed. My problem is it costs $1530... and that's just for the parts (~$1800 w/ labor & tax). I've just ordered one. It hurts, but my unresponsive brakes are starting to become a safety issue, because they're not there when I need (expect) them.

Good luck with yours,
Please let me know if the master cylinder helped,
Guido