I believe the mastery bonus for Resto is bugged.
If you have an active Lifebloom ticking and you cast a direct heal, then Harmony will increase subsequent Lifebloom ticks with its bonus.
An already active Rejuvenation on the other hand does not get its subsequent ticks increased, and must be recast in order for Harmony to take effect.
Why would these two act differently? This must be a bug.