Stereo in framebuffer, but not in processed framebuffer

[LReiter]

Hey everyone,
I'm currently using a modified version of [url=http://pastebin.com/2VEasjbu]this[/url] minimal example to get my Qt openGL app Rift compatible.
When I render to the framebuffer, it looks like this image (about right).
http://www.pic-upload.de/view-23131226/framebufferexample.png.html

When I process the framebuffer with the barrel distortion though, it looks like the second image.
http://www.pic-upload.de/view-23131225/processedframebufferexample.png.html

So basically I'm losing the two viewports and am rendering only one "behind" the "shader goggles". How could this happen? I mean, Im rendering the framebuffer to screen, am I not?

In the above posted code, shaders start at line 536. Relevant code for postprocessing starts at 655 or 614.
If anyone could help me into the right direction I'd be grateful.

The (I believe to be) relevant parts of my code are as follows:
http://pastebin.com/nQdud9Tc