I've noticed this behaviour on different Windows installation provided with different printer types.
I have sent to printer via gsprint a lot of pdf documents, each of them with different page number. I have seen that
the order in which documents are actually printed on paper doesn't always matches printing submission order; I mean
I can see a document of 20 pages to be still in spooling phase while another document queued after it is actually printed.
What I'd like to know is if this behaviour may be considerate "normal"... one would expect that documents are printed in
the exact order in which they're sent to the printer, but it seems that under some circumstances, Windows tries to maximize
throughput and prints documents in the order in which they become "ready to be printed".