256 landscape textures show up in Maps folder - why?

I encountered weird issue. When I open map with landscape, 256 textures files are dynamically created and show up in Content Browser, same folder as umap file. These files aren’t saved as assets on disks and one cannot simply delete it :wink:

Any idea what’s the cause? It seems to appear in 4.8.

I’ve noticed a similar thing, though only a single texture.

I got answer at Answers Hub.
It’s caused by flag Generate landscape Real-time GI Data.