Recently it came to my attention that some attacks, like the Guardian Staff 2 (Orb of Light) don’t show the orb animation when fired without a target. This way it is not possible to detonate the orb at a specific distance, since it is not visible.
The same thing happens with the Engineer Flamethrower kit 2 attack, as well as the auto attack.
//EDIT
Correction: When targeting a friendly target or non at all, the projectile flies downwards, making it disappear into the ground. This can easily be seen with Guard Staff 2 (see screenshot: https://imgur.com/Vowf5tC)