Can anyone explain this strange behavior with signed floats in C#?

Question

Here is the example with comments:

class Program
{
    // first version of structure
    public struct D1
    {
        public double d;
        public int f         


        

Answer 1

If you make D2 like this

public struct D2
{
    public double d;
    public double f;
    public string s;
}

it's true.

if you make it like this

public struct D2
{
    public double d;
    public double f;
    public double u;
}

It's still false.

it seems like it's false if the struct only holds doubles.