You can think of finding your first conTeXt bug as a kind of initiation, you are now officially anm advanced user :-)
It would be nicer if only I would be able to work it out :-)
There is a file named mp-spec.mp on your harddisk somewhere (and possibly more than one). That file is indirectly used for each metapost graphic in context, because it is one of the parts needed to create 'metafun.mem', that is then itself used by mpost while creating your graphic.
I think I found the mem file. In fact, I created a .mem file and when I substitute the old with the new one, nothing get printed out anymore. I'm getting really lost with all this unix-filename always repeating in different parts of the directory tree. I never know exactly what's happening. Any hint would be very appreciated -a-