I also faced the same problem.
As others said, If I deleted android:screenOrientation=”portrait” or overrided it with android:screenOrientation=”unspecified”, then the exception was gone.
And it seems that the front activity’s orientation follows the behind activity’s orientation.
I thought about it.
If the front activity is transparent and the behind activity’s orientation is different,
the display becomes strange.
So, I can understand why this check logic was added
However, I wonder that why this problem was not occurred in Developer Preview 8.0.0.