This is about the warrior rifle burst skill “Kill Shot”.
For example, if you use Kill Shot with only 2 bars of adrenaline and then refill your adrenaline with Healing Surge you can immediately use Kill Shot again, since level 2 doesn’t share a cooldown with level 3.
None of the other burst skills have this behavior. This could be an issue in pvp with players chaining multiple kill shots for massive damage.