Blocks that emit light have shadows on sides. They shouldn't, because they create light, light that should be stronger than the shadow being cast. I made glowstone pure white to display it best. This happens in the new snapshots too.

Mediafire link to resource pack: http://www.mediafire.com/download/t1vp2ulk28juin4/Default+Resource+Pack+%2815w47c%29.zip (didn't make it, just changed pumpkin and glowstone)