Actually, this is a normal part of the booking process. Before you can pay for something, necessarily that thing must have been reserved for you. This is done by creating a PNR with the reservation, and only once it is paid for does a ticket gets attached.

KLM actually offers this as a service btw, you can buy an "option" for a ticket to keep its reservation alive for some period of time even if not ticketed. This allows you to reserve the flight and pay for it at a (slightly) later date. Additionally, this service is offered for free (and for considerably longer) when booking with a BlueBiz or corporate contract number attached. Edit: case in point I just reserved a flight for the 26th this month and it will let me pay for that any time up until 48 hours before departure.