Screen.orientation returns different value from the actual screen orientation when "Auto-rotate screen" is disabled in Settings->Display.
The application starts in portrait orientation, but "Screen.orientation" returns "PortraitUpsideDown" when the "Portrait Upside Down" default orientation is selected in the player settings and the "Auto-rotate screen" option is disabled on the device in the Settings->Display.

Reproduced on:
Google Nexus 5 with Android 4.4.2

Reproduced with:
Unity Version 4.3.2f1 (0517a5ae8669)