xss_clean and base64

[eluser]redcloud80[/eluser]
Hi! I'm running CI 2.1.4 and I don't understand why this test fails.
I tried with many different image types but the output is every time FALSE

Code:

$base64 = [removed]iVBORw0KGgoAAAAN...";

echo $this->security->xss_clean($base64, TRUE);

[eluser]redcloud80[/eluser]
Cool, the forum too has stripped the base64 prefix lol!