Absent tentapillar

Recently I generated a few worlds and noticed that periodicly world generates characteristic turf pattern, but there is no tentapillar. I checked every other tentapillar present in that world and they work fine, i.e. every tentapillar generated has pair. However, I'm not sure if every world with similar event happening works correctly, so I decided to report it as a bug, especially since usually every world has 1 tentapillar in blue mushroom forest, which sometimes helps a lot to find mentioned forest. No mods affecting world generation were used, settings were default, except failed surviviors set to "none" on both shards and resources set to "classic" on both shards.