I have recently upgrade to LR6 from LR4. During my use of printing functionality with LR4 it has always been a bit dodgy on showing the correct page size in LR - but eventually after trying a few times it honored my choices.
Now with LR6 the work area for printing does not change at all - despite changing many times...
Printer setup (sorry in danish...):
but unfortunately LR's work area is showing this:
Anybody that has got hint to what is happening...?
I am using a HP c310a printerdriver.
Please go to the Page Setup in the bottom left corner in the Print Module and from there select the Paper Size.
Once done, you should be able to see the correct paper size on the screen.
Please let me know if it helps.