What I described is how it is implemented in code right now. The flag is used to affect the line-of-sight calculation for the source object in case of teleportation, but it is not used when calculating it for the target. For projectile skills, it does affect the line-of-sight calculation for the target object. Teleportation and projectile skills do not share the same code.
They do call the (same) line-of-sight calculation routine (the teleportation code even calls it twice; once for the source, once for the target), but it has parameters that allow the caller to specify what should be considered vision-blocking and what not.
