Some of the implementations of Equals, operator == and GetHashCode are wrong.

For example:

var x = new BsonInt32(1);
var y = new BsonDouble(1.0);
Console.WriteLine(x.Equals);
Console.WriteLine(x.GetHashCode());
Console.WriteLine(y.GetHashCode());

Outputs:

True
23866
1072716558

This violates the contract of Equals and GetHashCode, which states that when two objects are Equal, they should have the same hash code.

Another example:

var r = new BsonDouble(double.NaN);
var s = new BsonDouble(double.NaN);
Console.WriteLine(r == s);
Console.WriteLine(r.Equals(s));

Outputs:

False
False

To be consistent with the double data type == should return false and Equals should return true in this case.

There may be other examples, which is why this ticket says to check all implementations.