Version: 2.77 rc2 (linux 64bit)
Apologies if this has already been addressed.
How to reproduce:
Open the attached .blend in ver 2.76, note the background color in the preview
Open again in 2.77 rc2
In 2.77 rc2, the OpenGL preivew of scene strip has no transparency. This makes the strip look totally opaque, making OpenGL preview far less useful if one needs to preview scenes with alpha transparency.