This isn't a bug. It's been reported many times and even brought up to Yoshi-P. It's always been this way and they obviously know about it since it would be impossible for them to miss when designing it.

Yoshi-P has said that healing and resurrecting are part of Red Mage's role, but that only resurrecting is part of Summoner's role, or something along these lines. But Phoenix heals the party at later levels instead.

The heal is from Arcanist, which can become either a healer or DPS, so it's been difficult to remove it from them since the player's personal path may lead to being a healer.