No... this is a new thing.
There are now several quests that give you a vehicle exit button but do *not* give you a vehicle bar. For these quests, the [vehicleui] macro condition is false, but the UnitCanExit() API call is true.
I have asked the Blizz team to add a [canexit] macro so we can support that and the indication is that they will. At present, I can't see a way to make it work other than to not hide the built in Vehicle exit button... but that can be a real pain, too.
/sigh
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