I was testing some stuff yesterday and I shoot to an empty billboard ( this http://community.bistudio.com/wiki/File:Arma3_CfgVehicles_Land_MapBoard_F.jpg )and I noticed that:

• if you shoot in front of the billboard ( where you put a .paa ) bullets pass through because I put this in front of a building and when I shoot to billboard bullets hit the windows behind this
• if you shoot behine the billboard bullet don't pass through but hit the billboard

very strange :)