Float compare broke!

[Era Scarecrow]

 Most curiously while making unittests the asserts fail when I've 
confirmed it's working. The difference seems to be if it's 
immutable/const vs non, and why this makes a difference I don't 
see... Can someone give some light to this?

const float i_f = 3.14159265;
float a = i_f;
float b = i_f;
assert(a==b);    //passes
assert(a==i_f);  //fails