Indestructible Infantry Parachute Units?????

From what I've seen, when the air unit carrying the infantry is destroyed and the unit parachutes out, if there is a space in the same column within the defence set up (ie a square without a defence unit or lake, scrub etc) the infantry unit will land before it reaches the structures and fight as normal. However if there are no gaps in the column the infantry unit is floating along it will continue through to the structures. Then similarly the unit will land if there is a space between the structures or otherwise it will continue to the back row. Just my opinion but I think whatever the reason is, it does seem to be a glitch/error in the game because I find it difficult to understand why some cloaked parachute units get through and some don't? It seems to me once the air unit carrying the infantry unit is destroyed then the game will land the infantry unit at the next available open space within the column it is moving along irrelevant as to whether it is within the defence units or the structures and makes a bit of a mockery of the defences of the base being attacked.