The odd sounding MS-recording I mentionend earlier seem to be:
AMB_Urban_Madrid_Day_Pond.wav
AMB_Urban_Madrid_Day_Skaters.wav
AMB_Urban_Madrid_Night_Plaza.wav
I talked with stavrosound and he agreed, that something is odd about these files. It seems that something went wrong during the matrixed encoding.
According to stavrosound you can solve the issue by inverting the phase of one of the two stereo channels. I haven't checked it myself so far, but since he's quite experienced I trust him.
I don't want to blame someone with this post, so please don't get me wrong. These are three nice recordings and it would be a shame, if users wouldn't use these files, because they sound weird. So hopefully everybody can correct it and use it in future projects