Repro steps:
When I finished tending 5 patches, I received congratulations message from rock ("the gods will be happy").
I wasn't sure what type of reward I had gotten, so I rechecked my current quest log and saw that the quest was still open there, and it still said I had only tended 2/5 patches.
While reviewing the bug forums, my current skill finished training. It looks like that forced some type of refresh because it no longer appears in the quest log list at all, either complete or incomplete. it's just not there at all.
Noted only because it's not the expected behavior based on how the other quest completions have fired off.