Invisible background turns up inside alpha's

Hi,

I've got this problem I can't seam to work around 8-(

I've got an Ice-texture, which needs to refract and reflect a photo.
I've but the photo on a sky object, the sky-object has a compositing tag telling it: not seen by camera, but seen by rays:

OK,
It shows up through transparancies and in reflections, but...

I don't want it to show up through "alpha transparancies".

When you want to work with a sprite-layer, the sky will form a rectangle around your sprite, because it is seen by the ray that goes through the masked section: very annoying, I thought this was exactly why there's a transp. AND an alpha -channel ?

any suggestions ?

kindest regards,

Filip