It happened to me at a red light on my drive home on delivery night. I was freaked out that it may have malfunctioned so fast but I chalked it up to an anomoly. In the 7 months since then, it had only happened 1 other time and it was at a drive thru where I was waiting for a while. I think time stopped matters... it activates the actual red parking brake in case you forget that you're on autohold I presume. I haven't run any timed tests on this of course.

To be honest, auto hold is a nice feature in theory but it is not as intuitive as releasing the brake and going as normal. Even if you're stuck in traffic a lot I don't find it very helpful - without it, you're releasing the brake and don't have to hit the gas to inch up. On auto-hold, you're actually accelerating to inch up, then braking again. More hassle to hit 2 pedals to manage instead of without AH managing just 1.

Now auto-cruise control that helps you brake & accelerate in traffic - that's a much more practical option which doesn't yet exist here.

__________________
'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr