[palosanto]

I just gave it a try and it seems to be working for me. I put it in landscape through the android notification pulldown bar, then opened MSP which showed the library in landscape orientation. Then when I opened a piece it was on single page (but still in landscape - the top of the page now on what would usually be the left side of the screen) so I opened the 'select display mode' dialogue to change it to two pages. When that opened it was already saying 'landscape' for the tablet orientation so I guess that changes automatically once the orientation is changed in the OS. Then for 'display mode' I selected 'two pages' and it all seems to be working the way I'd expect - two pages shown in landscape. I then pulled down the android notification bar and changed it back to portrait orientation and MSP automatically went back to portrait and now says 'portrait' in the 'select display mode' dialogue again. If you go through those steps is there one that doesn't work for you?

Thanks but I don't understand why it doesn't work for me ...
When I open MSP after putting the OS in landscape mode, the library opens but still in portrait not in landscape like you describe, and the display mode dialogue shows also 'portrait' and no way to change it (no pull-down).  This is really weird ...
I tried to open the app settings cogwheel (from top right menu on the library page) and it flashes a couple of times in portrait/landscape and ends up in landscape but it flashes every two or three seconds and it's frozen so I have to reboot with great difficulty because it's totally stuck.
I'm puzzled about why it works with you and not with me on the exact same device ...

I've tried also the same steps on my Samsung Note tablet and I cannot reproduce your steps either. I get exactly the same result than with my Max 3 .... (even more weird)  what the f$#@