*Update*
So I'm aware the FiST is somewhat known for door lock issues. I discovered that if, when the door is open, I press down ever so slightly on the little catch mechanism within the assembly it powers down the ICE, etc, so presumably a spring isn't doing its job very well within the mechanism.
I'm thinking that another potential fix would be to bend the striker on the door frame down a little in the hope that in doing so the catch would then be forced towards a little more, enough to tell the car the door was open.
Any thoughts on this or similar experience would be great!