with IM 6.3.6 Q16 on windows i run the following command:
convert *.jpg -average out.jpg
and my result, while resembling an average of the images is in fact nowhere close. running the same command on an older version last fall [sorry, don't remember what version it actually was...] produced the correct result. see the difference:
Correct version:

Incorrect version:

any ideas what happened here?
aaron