Zomboss + Healer = Unwinnable

I just lost all three matches against Penny's Pursuit Zomboss on the lowest difficulty setting with my level-7 Shadow Plants and Pokra.

The reason?

A single Roman Healer gave Zomboss that regen status, and long after the healer died, his health bar just continues to drain at a crawl, all while that atrocious healing sound just keeps ringing loud.

This is clearly some kind of oversight by the developers.

Won't be getting any Seed Packets for anything from Penny's Pursuit for two whole weeks because of this.

What a disappointment.