Its a bit like an MOT advisory. They found a fault, but it can be fixed easily.
NCAP still gives the MG3 a 4 rating, so that has not changed.
Would I buy an mg3 knowing it has a fault, certainly not..
But as for pulling it from Motability, that is their decision. Given its only a minor fault that can be fixed, a simple solution would be to take it off until its fixed.