Another dynamic could be that especially on longer trips that the DME decided to do a tank leakage test and then didn't bother bleeding the pressure, not sure if it normally does or not, and then of course it will much longer for tank to vent when the cap comes of.

__________________
1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)