gunnergoz
Cat Herder
This happened to me in one game. I killed off a barbarian galley that had captured someone's floating settler unit. The settler converted to mine. But then I could not move it whatsoever. Finally I tried moving another land unit onto the water, went over to the settler and paired them up. I could then float the two away and the settler was on a later turn able to disconnect and land itself with no problem. The unit pairing system can be kind of kludgey at times, even with land units I've seen the attached support unit stay in place until the end of the turn, then it rushes to catch up with the combat unit it is linked with.