It doesn't matter if you crouch or not, or where your cursor points on a water-loggable block (if you point at the exterior of these blocks, it should be placed on the adjacent block, not inside) If you make a floor of slabs or stairs or something, then it's almost impossible to place water above the floor. It would make sense if the slabs were on the bottom half of the block, but not when they are on the top half, when your cursor is on the exterior faces of such a block. 

That, or crouching should allow the old behaviour, so that you dont have to temporarily add a completely solid block nearby just to place a water source block on the outside of a slab or something.