Comment # 4 on bug 1152385 from Wolfgang Bauer

(In reply to Cor Blom from comment #3)
> (In reply to Wolfgang Bauer from comment #1)
> > The duplex option should be in the standard print dialog (where you can
> > choose e.g. the printer) on the tab "Options".
> 
> That is what I meant. Sorry if I worded it incorrectly.

Well, you wrote that the option is missing (under the advanced tab).

> Under Options > Options I can set duplex printing, but I cannot select "Long
> side" and "short side". They are grey.

They should only be grey if the printer (or driver) doesn't support duplex.
So this could either be a bug in Qt, or in the printer driver.

I cannot test as I don't have a printer that supports duplex.

> Because you said the other bugs are different, I checked a Leap 15.1 here,
> with the same printer, and there it is working correctly. I can choose "long
> side" and "short side", so it's happening only on Tumbleweed.
Leap 15.1 doesn't have these changes yet, only the patch to fix 
https://bugs.kde.org/show_bug.cgi?id=395517 .