It is rendered in the Humanitarian rendering.

Although it has been mistagged as a cultured lawn (looks like the main tag should be natural), I can’t see why it shouldn’t render as something other than water, at least on the basis of being an inner in the mutipolygon relation for the lake.

My guess is that the other renderers aren’t really processing the multipolygon, and don’t consider that landuse equates to dry land.