Door handles on these seem to be rather fragile, my old Rover 400 was the same & i did manage to sheer off one of the back door handles due to it being frozen solid!...oh those were the days! lol
My ZS has been a pig to get in during this cold snap, but my trick is to pour some tepid water along the edges of the door frame & a tad on the door handle & it works a treat!
PS Southside, i know what you are talking about mate the interior door lock facility button
mine seems ok so far!