When I try to render a map or update an old one all the mushroom are rendered in a wrong way. There are some problems also with lava lakes just under the surface. In the screenshot all the red giant mushroom appear as circle with a dot in the center and the lava lake in red is actually underground.
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Resolved as a duplicate of MC-132269, it seems to be the same issue
Confirmed in a new world created in 1.13-pre5.