Original 2001 version has a feature that may
be your problem in some cases. For your
convenience after you edit any numeric value
and leave it (move cursor to another one)
AVIfrate tried to calculate new frame rate,
total duration etc. AND unfortunately this
might change the previously values due to
int->float->int calculations and rounding.
So, now I decided to change this logic and
in AVIFrate 2009 the fps value is calculated
but doesn't affect scale/rate anymore.