When application is starting to launch, orientation seems to be correct, but after splash screen loading, orientation is not respected correctly.
Regression from 5.4.0a4.

Repro steps:
1. Create empty project;
2. In "player settings" set "Portait" orientation only;
3. Build to UWP platform;
4. Deploy application to Surface 3 tablet, but before set it to "tablet mode".

Whatever orientation you change, those changes are not respected and don't make any impact when build and running the project.

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UWP platform (Universal 10): orientations are not respected when set in Visual Studio's package manifest. Issue reproducible even with a new non Unity project, created in Visual Studio.

Workaround:
Orientations can be set in Unity player settings or can be forced by script.