Another long standing issue that devs have squashed in an upcoming Simulation update.
Regrowth 3-5 teched with Heal Recycle III (-10 to recycle). Regrowth has a 10 second delay and the Heal Recycle causes a zero delay. This tricks the spell to behave like a Bolt (Flame, Prime Bolt, etc) which repeats over and over until stopped. It'll just now cast once like it's suppose to.