If you aim a launcher at a wall, the explosion prediction will show you how it looks like if the weapon exploded in the wall, but the actual projectile would explode against it, not on the same tile.
It's probably how it's supposed to work (after all, explosion prediction shows the explosion at the point you're aiming at, not where the explosion would end up), but it's something that's very easy to unconsciously understand but never really consciously notice until something you calculated shouldn't happen happens anyways.
And so one might end up aiming the target of an explosion to be barely out of range of Cogmind, but because it actually explodes in front of the wall it hits, you get hit by the explosion anyways.
(That's how i once got hit by my own ST in the very last area.)