I've solved my problem. Finally, strace and the openmediaplayer source code helped me a to understand that the issue was related to mafw.

Lucky guy I am, my intuition led me to reinstall mafw-gst-renderer package (which I felt was central in the mafw set of packages):
(I don't use apt-get) as root: I guess a pre/post install script from this package did the trick. Next time, I'll track /etc/ files using Git to hopefully see which change on which file solved my issue. Can I call this "blind-hacking"? Like it though!

Does anyone experienced the same?