Is this a bug or something I have not understood? I have observed that occasionally in some cities that no matter what I do, the computer puts a specialist into the bottom slot, sometimes more than one, even with small populations, the result being in one particular case that I cannot grow beyond size one.Everything seems normal otherwise. I cannot find any logical explanation for this. Every time I move a citizen on to a tile, it is moved off again by the program next turn. Why?

Can you post a screenshot or saved game?

I can't think of an explanation for the stunted growth, because as far as I know that's not supposed to happen. But if you are using the Mercantilism civic, or if you built the Statue of Liberty on the same continent, then a city has a free specialist (or 2, if you have both of these things). This means that you basically have an extra citizen that doesn't consume any food, BUT this citizen must be assigned a specialist position and cannot work a tile. If you mouse over your specialists, you should see one or two that say "Free Specialist."

Now if such a city shows a population of 1, then you should still be able to work a tile outside the center. If you try to work more than one, then yes, it will revert to your "Free Specialist" instead.