png alpha in 3d view

I’m new to blender but I’ll try to tell my problem as well as I can.

I’m trying to make a 2d animation with lots of png images. I import images as planes and I can see the planes on the stage in 3d view. Some png images work fine without any problems but some dont. I think small images (like pieces of characters) work well but larger images (Backrounds etc.) dont. They appear as simple planes with nothing on them. So I cant see the image and because of that I cant see through the invisible bits. As I use these large images as backrounds, it’s quite difficult to set anything up cause I cant see where things are. Though everything renders just fine when rendered, its just the 3d view in the work space thats causing trouble. And it’s really a pain in the butt to render an image just to see if anything is anywhere near where I’d like it to be.

I didn’t have this problem in blender 2.64 but I upgraded to 2.66 and now this happens.

Is there anything I could do to fix this or is it a bug in the program?