Of course they use the FF number to post to Qantas???? They do automatically post if you wait long enough.. They used to post within a week, but recently it has taken much longer.
And what makes you so sure that it is Jetstar, and not Qantas where the issue lies?
I've never had points from JQ flights post automatically either, and I'm currently still waiting for points from a flight on 2 Apr to post - which I've been chasing up for 6 weeks. Meanwhile, points from QF flights a couple of weeks ago posted before I took off, while points from AA and JL flights at the start of May posted within 2-4 days of the flights. If the issue lay with QF, surely points from any flight would be delayed, but it only seems to happen with JQ.