To get around the slow population growth with the Yor I purchased what Colony ships I could find, then i would fly them to my colonies in order to gain that population. (When there are no more worlds I can colonize with them).
Now when they are in orbit, I convert them to constructors the game tells me how long it will take, it is usually a turn. Now when that turn is done. The name of the ship indicates that it is a constructor, however the special property of the ship still indicates that it is a colony. If I try to launch the constructor it asks me how many people I want to load in it as it was still a colony ship.
Waiting an extra turn to use the constructor appears to solve this "hybrid status" of the ship.