Image::place() Unexpected output with transparency image

[romanmatyus]

Code:

$tux = Image::fromFile("http://upload.wikimedia.org/wikipedia/commons/a/a1/Tux2.png");
$firefox = Image::fromFile("http://people.mozilla.org/~faaborg/files/shiretoko/firefoxIcon/firefox-64.png");
$tux->place($firefox, '100%', '100%', 50);

should generate:

but generate: