Using Mpeg4/H.264 output with Sink Writer gives output with frames upside down

I've written a simple application that is based on the Sink Writer sample found here:

http://msdn.microsoft.com/en-us/library/windows/desktop/ff819477(v=vs.85).aspx

When using the default encoding setup, i.e. with encoding format set to MFVideoFormat_WMV3 and creating a writer based on 'wmv' file extension, I get an output as expected. 

However, if I change the encoding to MFVideoFormat_H264 and create a sink writer based on a '*.mp4' file name, the output video has the frames flipped upside down. The output file looks otherwise to have been generated as a valid MPEG4/H.264 file.

EDIT: I get the same flipped effect if I change to MFVideoFormat_H264 in the original sample mentioned.

Why is this happening - are there any additional settings I need to set to get my MPEG4 frames appear non-flipped ?

Regards,
Leif