Recently, we had a question about whether a terraformed world can be turned back into a colony by landing a colony ship. So, we took a second look at the programs in their current state and figured out that Worlds listed as Terraformed and Homeworld are not susceptible to recolonization. All other types of terraformed worlds ( Pirate Havens and Nomad Platforms, etc. ) ARE able to be recolonized.
This is not a new feature. It has been this way since the beginning of the game in 1982.