When I try to heal a low level character with my druid it downranks my heal similar to how MOTW works. A Rejuv on a level 1 only ticks for 18 hp. I’m casting a rank 15 rejuv. It does this with all addons disabled. Nourish still heals for the correct amount so it seems to be being caused by the HoT. It does this in both resto and balance specs.
I asked a friend and their rejuvs are getting downranked too.
As far as I know this is intentional behavior. As HoTs are considered “buffs” they get automatically downranked based on your targets level. I believe this interaction was changed with downranking changes in patch 3.0.2.