Taric w does the same. After linking, whenever one of you are in combat, the moonstone will keep applying.
Taric's is the same root cause bug as Seraphine. We caught the Taric one before Preseason, but not the Seraphine one. Someone is looking at it, so thanks for all the updoots and awareness.
Taric's was even more abusive, because he didn't need to cast any spells, just have a W link active and it would permanently go off.