gcd with doubles

[Alex via Digitalmars-d-learn]

Hi, all.
Can anybody explain to me why

void main()
{
        import std.numeric;
        assert(gcd(0.5,32) == 0.5);
        assert(gcd(0.2,32) == 0.2);
}
fails on the second assert?

I'm aware, that calculating gcd on doubles is not so obvios, as 
on integers. But if the library accepts doubles, and basically 
the return is correct occasionally, why it is not always the case?
Is there a workaround, maybe?