symbolic isequaln command doesn't work for the Folium of Descartes?

Gilat, MATLAB An Introduction with Applications, Problem 11-7 using Simbolic Math

syms x y t 
x=3*t/(1+t^3);
y=3*t^2/(1+t^3);
S1=x^3+y^3
S2=3*x*y
isequaln(S1,S2)
S3=simple(S1)
isequaln(S3,S2)

yields output:

 S1 =
(27*t^3)/(t^3 + 1)^3 + (27*t^6)/(t^3 + 1)^3
S2 =
(27*t^3)/(t^3 + 1)^2
ans =
     0
S3 =
(27*t^3)/(t^3 + 1)^2
ans =
     0

Obviously TRUE but Matlab says FALSE

[Azzi Abdelmalek]

What is Obviously TRUE ?

[Charles Griffin]

That S2 is equivalent to S1 or S3.

[Star Strider]

R2014a gives me 0 for the first isequaln and 1 for the second.