I would assume that is a normal safety feature. I can't open the back of my Escape with the engine running either.
My Reserve rear lift gate opens with engine running, but must be in Park, with/without doors locked...by pushing the button, lower left, next to round light control.The other day I was dropped off at school, when i went around back to open the rear liftgate the switch wouldnt release. The MKC was then placed into Park and still it wouldnt work. The engine had to be turned completely off for the liftgate to open.
Is this the case with all SUVs and is there any workaround? Thanks.