Yeah, you might think so, but if my code has the same problem, why does it not suffer the same problem calling numerator or denominator on "$s"?

I mean the output is, I believe, what would expect if it was working correctly:

n = 1, s = 1, num=1, den=1
n = 2, s = 5/2, num=5, den=2
n = 3, s = 13/3, num=13, den=3
n = 4, s = 77/12, num=77, den=12
n = 5, s = 87/10, num=87, den=10
nums=1, 5, 13, 77, 87
dens=1, 2, 3, 12, 10
[download]

Hmmm...not sure but it may that the original example that "worked" didn't really produce the right output or wasn't doing the right computation.