I believe the "locking up" issue comes like this:

When stopped with Auto Hold engaged, if the driver lifts off the seat enough (e.g., to get a wallet out of the back pocket), the transmission will automatically shift to Park. Presumably a safety feature so the driver can't depart the car while still in Drive.

If the driver doesn't notice the change in transmission status, then it's freak-out city when the light turns green. Not a complete disaster, but just another reason that I rarely use this feature.

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2008 X5 4.8i, Jet Black, Tobacco Nevada leather & just about everything else (no vent. seats, no 3rd row)