I have seen several posts on this issue, but no resolution and it appears to be an problem
It appears that the landscape checkbox in printer maintenance overrides the Portrait/Landscape setting in the RDL
This only appears to be an issue if you are using server printing/auto print. The only way I have managed to work around this is have an alternative printer setup in Printer maintenance with the same network path and have the landscape checkbox checked. We then print using that printer.
Of course if you have multi-site and you want to achieve auto print, the data directives start getting rather messy really fast instead of using the workstation printer assigned to the user.
I have to say it over complicates something, that to be honest should be rather simple. At the end of the day not all users want or need to do a print preview.
The other solution is don’t create any reports that you want to auto print in landscape!