When standing in a block adjacent to a fence, facing the fence and placing a block at head level, the block will be placed even if there is a player.

What was supposed to happen: Block should not be able to be placed

What actually happened: Block was placed

This affects signs too, if you place a sign onto the fence, the text input GUI will not be opened.

This can be used to exploit the TNT-look-through-blocks trick.

Screenshots show how to reproduce the bug. (1.place fence(s), 2 stand in the block right next to it, 3 place block (works with the bottom block as well))