I don't know when it stopped working, but here's v20.
And here's v21.
In the first of those three, the (wrong) result was echoed twice. In the second, the result is just wrong.
v:\> set /a zz=1/3=5 0.33333
v:\> set /a zz=1/3=5 5 5 v:\> set /a zz=1/3 0 v:\> set /a zz=1+2 3