[test printer: Samsung Xpress M2875; test OS: Debian Jessie]
When I try to print something on DL Envelope paper size, it has to be earlier configured in system-wide settings (http://localhost:631, system-config-printer, etc.). I mean, that in File->Print->[select printer]->Properties->Paper size I can't see all sizes, but only suitable with default (currently configured in CUPS) (assume that it's 'Plain') paper type. So that I can't print on DL Envelope, because it's not listed.

I have to select (assume that using system-config-printer) in Printer Options:
- page size: DL Env.,
- paper type: [thick or not] envelope.
You can see that there's condition: I can't save option [page size]=[DL Env.], if paper type isn't compatible. There was no such condition in older PPDs (eg. when trying to print DL Envelope on older Kyocera printers, there weren't such problems).

After that I restart LibreOffice and try File->Print->[select printer]. Wow. I see the magical DL Envelope. If I click Properties, then I can see all page sizes available for [thick or not] envelope paper type.

I think that it's only a workaround, because normally I need superuser permissions to change CUPS settings.

I've tried to test it on Windows, but after click on Properties, there's only configuration window from Samsung.