Unity 4 BETA: iOS: Texture2D ReadPixels not responding to bound framebuffer

In Unity 3.x/iOS I've had success with retrieving texture data from an image rendered on the device with the following process:

[Unity]

• Create Texture2D

• Pass texture handle to device

[Device/OpenGL]

• Create frame buffer and bind texture

• Do custom texture rasterisation into framebuffer

[Unity]

• Set texture framebuffer as active

• Call ReadPixels() on Texture2D to pull hardware texture into memory

• Restore Unity/native framebuffer

Now using the Unity 4.x BETA/iOS ReadPixels() pulls in the full Unity scene render and not just my custom stuff. After reading the docs (again) there is a mention that ReadPixels() on mobile devices is deferred until the end of the frame, so I've tried a co-routine approach with WaitTillEndOfFrame() and that still brings in the full Unity scene render.

I've also had a tinker with Render Textures but they aren't responding at all (there should be no need for a RenderTexture as I just need a hardware texture handle).

I'm wondering if there is a change in ReadPixels() that forces a read from the Unity context (even though I'm explicitly telling OpenGL to set my framebuffer as the active framebuffer) and overriding my approach? I think I've tried everything to counter any possible timing issues..

Any suggestions would be greatly appreciated!