Yes, I know what you are talking about.  I cannot paint on an eco, just populate an eco because I have Esprit, but I have had the same trouble from time to time.  I do not know what causes it.  I usually clear, save, and then repopulate, highlight the terrain in the world browser, move the eco and it has usually gone away. 

 

I assume in my case it has something to do with resources and Vue not writing to or reading the temp files correctly.

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