Image transparency after merge

[ivoilic]

So basically I have two lines that generate an image from png and then preserve the transparency of said png.

$bub1 = imagecreatefrompng ("Energy/$energy1b.png");

imageSaveAlpha($bub1, true);

This works by itself when generating just this image.

But when combined with another image:

imagecopymerge($image, $bub1, 680, 40, 0, 0, 50, 50, 100);

It fills in the back ground around the image and the transparency is not preserved. 

Why is this and how can i fix it?