crude pine
As you can see in the video, the smoke screen is deployed before even half of the T8M's missile flight time has elapsed, causing the T8M to lose its lock (please look at the Aim icon above the T8M). However, the SA missile still hits its target as if it were a fire-and-forget (F&F) missile, and that is where the problem lies.
keen meteor
The aiming does break, but I think since the tank doesn't move and the missile is still flying they connect. If your tanks had moved it would have probably hit the dirt.
Missiles are still objects and if they hit something they will do damage to it.