Barrier Block Issues

Whenever I place a block on a barrier block, if the block is facing north, or west, the block's texture becomes invisible. For instance, a tnt block is placed when facing in the west, or north direction: It is still a tnt block, for it still explodes: but the texture changes to the same of that of a barrier. If placed while facing south, or east; the texture is normal. Weird, Huh?