I don't know if anyone else has noticed yet (I am sure someone has), but there are massive non-buildable areas on the new islands. Essentially, the entire western section and northwestern section of the Ice Island is non-buildable. When I say "massive", it's 8 squares in from the western edge of the island and 6 squares in from the north edge of the island in the northwest corner. This amounts to getting 2/3 of the area that should be buildable on this island.
On the Rainbow Island, there is a section just south of the water that is non-buildable and is 6 squares wide coming from the eastern edge of the island.
I haven't finished clearing the rocks on the Gothic Island, but the center eastern square is basically entire non-buildable. If you attempt to put a habitat here (I used a Big Electric Habitat for all my testing), it will be half into the center square of the Gothic Island before you can place the habitat here.
I have already sent two notes to SocialPoint about this - one about the Rainbow Island and one about the Ice Island. I am feeling quite ripped off at this point; I expect them to fix it and I have told them as much (politely - there is no more vitriol in my messages to them than there is in this message).