Firing a Double Splitter point blank at another tank does nothing. It just skips the firing sequence and goes to the next turn saying 0 damage. This is 100% reproducible.
It's not supposed to hit. I mean, even if it was Point-Blank, it would probably hit you also. It does the same for weapons, such as, say Cactus. Spread-Projectile type. My guess is that the...effect, I guess, was there to prevent things such as Cactus trick, and Wild One trick. Here's a video depicting the Cactus trick in the first ShellShock. You can see why they wanted to prevent it in ShellShock Live 2. Very helpful there.
It's not supposed to hit. I mean, even if it was Point-Blank, it would probably hit you also. That was the idea, since I only had like 5hp. Anyway, if it's intentional...it seems a bit dumb but oh well.
If you put weapons such as Double-Splitter, or regular Splitter in the ground (I mean the turret is actually penetrating the ground, like it would be 359 degree angle on a flat map, or something), then it just wouldn't activate. It makes sense.
It sure did in the first ShellShock. Which led to Cactus Trick [130 Damage] and Wild One Trick [...I think it was...200?]. So my guess was that it was manually disabled in the second ShellShock. Which really isn't a problem due to stuff like Angry Birds and Seagull.
In SSL1, if you fired a cactus just under the ground at the very bottom of the map, where the ground is indestructible, the game would make all 13 cacti balls explode right in front of you. If you did this under a player, it would give you an instant 130 points of damage. This doesn't work with destructible terrain, as the cactus would destroy the ground and be able to spread. The exact same thing applies to wild one. They tweaked something in SSL2 to prevent this trick/exploit from happening. Otherwise, they would have two more weapons that are extremely OP in addition to Seagull, etc.