Sorry you are wrong.
In the interests of all I have gone through the process with one of my bookings and captured screen shots as below. I do not profess to an expert but as someone who flys around 130-150 sectors per year mainly QF and OW with SQ and VA being not far behind I am reasonably confident in my understanding of QF fare types and rules . As
@justinbrett states above people seem to be getting confused "refund" and "change" fees
This is the evidence.
Go to you booking and select cancel this will pop up will appear, select voucher
View attachment 206328
This screen will appear.
View attachment 206329
Once the voucher is in your QFF account click on it and follow the bouncing ball, I did not get a screenshot
put in new search parameters, my screen shot was to early, I ended up selecting 9 Mar 20.
View attachment 206330
Select flight
View attachment 206331
Follow the bouncing ball until the final payment screen is reached and look at the detail
View attachment 206332
Now my maths might not be that good but the original credit was $140.71 and the additional charge to my CC was 235.68 (image above) that totals $376.39 which is give or take a few cents is close the expected Itinerary price.
I hope this makes things clearer.
I will now be going back and cancelling this booking and turning it into another voucher for future use.