Yes, this probably affects many other gears as well. You could also fire arbitrary projectiles and would not collide with them while in mid-air.

For example, you could fire a mortar stright up and when it comes down, you just make a double high jump and don't collide with the mortar (you still might collide with the clusters if you're unlucky and fall on the groud too early).

I made falling flames take out hogs on rope and everyone freaked out.

I do have it flagged though, and lua can enable this behaviour. ClimbHome uses it to make fire cakes scarier.

Yeah, falling flames on hogs can be very frustrating indeed. This is also partly from the fact that flames are not strict in terms of turn-based strategy; they can fall down in mid-turn without doing anything. But I already talked about this topic.

But most other things like a bazooka shell could still collide. Especially the mortar trick seems very odd.

Making things hit hogs in motion is kinda tricky 'cause moving hogs aren't "solid" and part of the landscape.
The usual trick is to make an invisible explosion that searches for hogs nearby and keep doing it over and over.
This doesn't quite lead to the same results depending on when the explosion check occurs. A repeated check on nearby hogs could be done in the falling code and a collision flag set if within a certain radius. This has a cost of course. Maybe not too significant of one nowdays.