At QKL and ZWS there are no check-in machines. Recently I did an Airail MR. One CSA smiled when he saw my itinerary. Later, the other one was quite snappy and denied issue of my bp for the second return FRA-QKL ("I can check you only in for this flight and you have to come back later.") and wrote down my name to ensure that I was factually on the train to FRA. BTW: Be aware that there is a check-in deadline at QKL. If you come in late from FRA the deadline could be passed. I would not wonder if this charming CSA pleasurably refuses checking you in because you are obviously on MR and check-in deadline has already passed. Vorschrift ist Vorschrift!