MySQL ignores UPDATE when data is the same?

[solitario]

Hello all.
I just discovered (correct me if I'm wrong), that MySQL ignores an UPDATE when the data is exactly the same as already in the database.

For instance, I have this query:

UPDATE cms_users SET user_email="[email protected]", internal_notes="blah blah blah" WHERE cms_users.user_id=8

I pass that to a class function which executes the query and returns the number of affected rows:

$affected_rows=$database->execute($query);

Then I was testing it:

/* DETERMINE IF THE QUERY WAS SUCCESSFUL */
	if(
		$affected_rows>0
	) {

		/* SUCCESS */
			/* REDIRECT BY CALLING THE FUNCTION WHICH BUILDS A REDIRECT URL */
				header('Location: '.admin_redirect_url('thank'));

	} else {

		/* FAILURE */
			/* REDIRECT BY CALLING THE FUNCTION WHICH BUILDS A REDIRECT URL */
				header('Location: '.admin_redirect_url('err05'));

	}

Once I actually changed the data, the value returned by the class function went from 0 to 1.

So my questions are:
1) is it MySQL or PHP which is doing this?
2) is there a way of "forcing" the database to update, without say, adding a timestamp?

Many thanks.