In any case it's odd to repurpose pond polygon as park polygon, and I agree that if the pond still exists then probably it should be still mapped.

As for additional park being created, that sort of confusion is expected if there are multiple overlapping landuses. That's another reason why within park instead of landuse=grass it'd be better to use landcover=grass (that shouldn't be rendered the same as landuse).

This area is particularly messy as some parts of it have 3–4 overlapping landuses.