Zir’an’s heal BBS can target minions at full health, which does a whole lotta nothin’ unless you have something that triggers off it - say, Scintilla, which triggers on the BBS cast regardless of whether or not it healed anything.
After playing a Sunbreaker and then losing it, my BBS reverted to Zir’an’s heal BBS. However, during a clutch moment at the end of the game, I discovered I could no longer target friendly minions to trigger Scintilla’s heal.
I don’t know if this behavior is because Tempest is an AOE effect with no target, while Zir’an’s is a single-target minion spell, but either way it lost me a game, and may need to be fixed. Granted, running Sunbreaker in Zir’an is an ongoing experiment that may have lost me the game anyway, but still…
TL;DR Sunbreaker screws up your BBS when it reverts.