I can click through certain blocks, like dispensers, and slabs, by aiming at the lower half and the highlighted block becomes the block below!

All you need to do is just start bridging, if the blocks under are out of reach you will find this issue cause you to fall, if you are about 2 blocks above the ground or blocks beneath you can see you aim at the block your standing on and the block underneath being highlighted.

I am not sure but it might be related to view bobbing!