If I'm not mistaken, this all goes back to the fact that simpabs calls
cabs. There is a reason that abs and cabs are distinct -- one is a
mathematical (simplifying) function, the other is a form-changing function.
simpabs should never call cabs. (This bug was apparently introduced some
time before Maxima got into sourceforge; it was not in MIT Macsyma when I
was working on it.)
-s