We wan't to support both platforms, because the code is 100% portable to Windows Phone 7 from our Windows Phone 8 project, but i have noticed a strange problem.
So to support both platforms we need to create WP7 project and it will be installable on WP8, but:
On small devices like WVGA, application looks normal, but when i open it on 720p it doesn't use 100% height.
Example:


What the hell? If i open the same xaml in WP8 project all works perfect.
P.S. Full design is rubber - no hardcode in pixels or %. How to fix it?