Why is Matlab not writing out all the terms in an expansion?

I am trying to expand some polynomials, and I typed: >> y1

Syms s1 s2 s3 s4;

y1 = (s1^2 - 4*s2 + 8*s4^(1/2))*(4*s2 - s1^2 + 8*s4^(1/2));

>> expand(y1)

And Matlab told me that

ans =

- s1^4 + 8*s1^2*s2 - 16*s2^2 + 64*s4.

But I'm pretty sure the answer should have six terms, so what's happening?

Thanks.

[Azzi Abdelmalek]

The result is correct, just check it again

[Lillian]

Oh, you're right. And I typed in the expressions wrong. Thanks.