"sum" quotes its arguments -- what's up with that?

I don't have time to write a long answer right now, but this issue has
been discussed at length.  The basic problem is that Maxima has no way
of saying that the first argument of 'sum' is evaluated in a scope
where the iteration variable is locally bound without using defmspec.

Consider:

   i: 25$

   sum(i,i,1,3) => 6   current behavior

   sum(i,i,1,3) => 75 with your suggested change