This turned out to be a lot more complicated than expected. There were a lot of PDFX-related changes in 6.5.1709.4 related to working around a bug in the driver having to do with paper size designations. The workaround involved setting up custom paper sizes to match the desired standard sizes. That had the unfortunate side effect (not noticed until today) of interfering with the ability to switch to landscape. Anyway, once I figured that out, then the task was to find another solution to the original problem. After trying various things, I noticed that there was a driver update (see link below) and at some point after updating, things seemed to sort themselves out. But I haven't had a chance to thoroughly test it. I also haven't had a chance to write up the notes for all the things that have changed in 6.5.1724 (including the XTREE filter changes discussed
here). But if you're brave and want to try it out, I suggest starting with just the A-Shell update. It might actually solve the problem without having to update the driver. If not, then update the driver as well. (There's no harm in updating the driver, but it's a bit of a pain to have to get all your installed PCs to update, so it would be nice to know if it was really necessary.)
And if you start smelling smoke, shut it down and go back to fighting the giants in the forest.
ash-6.5.1724.0-w32c-upd.zipPDFX9SA_sm.exe (9.4.364)