I have the exact same problem in my '05 X5 3.0d. I hadn't noticed test driving because I hadn't driven it long enough for it to warm up properly I suppose. The problem doesn't happen at all if I switch to sport mode, which makes me have a little bit of confidence that there's SOME chance it could be a software issue.
I will try the reset trick today and let y'all know if it works.
Cheers,
Scott.