Thanks to all,
@ Toby: I know you can prefix the orientation, but it was just that feature to let the user decide for using in portait of landscape mode.
@ Serge: Indeed, I already use that RemovePreviousPages after login, but it's what Jake says, The app is restarting.
@ JakeBullet70 : I hadn't noticed that, Directly.
@ Agraham:
I understand it's meant to work that way.
Is it strange if I compile my app twice. Once as a landscape and once as a portait variant. In that case, the user still has the choice of which app (s)he wants to use.