Well, there was no "fix"...it should simply work.
A workaround you might want to try is to create a new form, which will use the pdf emulation, and use the incoming pdf as data. It will have two pages: one portrait, and one landscape. Then, you will put a condition on each of the pages. Look for something that differentiates a portrait page versus a landscape page, and make a text conditions based on that, then put them on the portrait page and the landscape page. As for the content of those pages, all they will do is display the current page of the pdf, which can be done by right-clicking on the pdf in the data selector, and choose "Set as Background". Do that for both pages. Once the form is done, send it to Workflow.
With this, the page should properly switch between portrait and landscape if you use that form in the Print Using Windows Driver output.
Let us know if that works!
Regards,
Raphaël Lalonde Lefebvre