I have brought gnats from HAM to my ROG world so I can farm their mounds for minerals. However, later I chose to resettle in SW and needed them to keep making lamp posts without going back to HAM or ROG worlds for iron. It didn't end well with the last update as I lost all my gnats to this weird bug (see steps to reproduce).
1. Get gnats on you when their houses are destroyed before dusk. 2. Run to skyworthy (mine was located in Slanty Shanty). 3. Use it just before dusk starts so while animation plays dusk comes (I did that unintentionally). 4. When you arrive to SW world, gnats are gone. They are not present near Skyworthy in previous world or near their mounds' former locations.