Paintings no longer able to be placed on signs

Me and my friends used to put signs on pressure plates, then paintings on the signs to make computers, when I tried that method after the update, even with a shift click, I am not able to do it, the previous placed paintings remain placed, this method is pretty much the only good way to make a good laptop, if I use a trapdoor, the trapdoor would open when the pressure plate is activated, which happens often.