Absolutely right!!!! My guess is that they treated it as a reissue of the OWE ticket and waived the change fee! I saw QF do that to someone in LAX and intervened -- they were going to send the poor person by coach LAX-JFK when lots of 3-class F available but no A (and it was a mis-connect due to late arrival into LAX). Agent was very miffed at me for giving the other passenger advice (and causing them much work as well as costing QF some money), so much so that they pulled up my profile (presumably to annotate with some nasty comments). Then their tone changed, and service became much better. Got me curious what exactly it says there (I have no idea, I am not CL but do fly a fair bit, mostly in paid F).
I wonder if this is routine or airlines do it deliberately? I had a re-route by one OW airline onto another OW airline that was incorrectly prepared and the receiving airline was convinced that it was deliberate (to deprive them of some revenue); luckily they fought it out behind the scenes and I wasn't affected. OW is an "armed truce" kind of alliance at times.