I had a Pioneer on a Transport and I was heading towards a spot where I thought I could create a settlement, and I noticed that the Create Settlement action (or whatever it's called--I just tried to alt-tab back to the game to check and it crashed) was lit up. So I clicked it and was able to create a settlement out in the water. I couldn't build any improvements, which limited growth due to housing shortage, but I was able to train units.

Correct me if I'm wrong, but this seems like a bug.