hello
actualy is not a bug, more a game mechanic. How it works:
- When town has the demanded cargos, will try to build new houses (even when some houses not finished yet);
- The count of finished houses (current population) plus the unfinished houses (being built) gives the
potential population;
- Many players when see the potential population above the server goal, stop vehicles. Why? because they don't want town to build new buildings (not needed anymore) but only finish the being made (unfinished). Not delivering cargo demanded (stopping vehicles) makes sure that the town don't rebuild an existent building, possibly putting population below the desired goal.
Well, I hope the above lines makes it understandable. And I think there's no way to prevent this so, the best is to know the potential population mentioined above. Vanilla OpenTTD don't provide tools for this, but you can use the
BTPro client
that gives that value in each town window.
Hope it helps and any doubt, feel free to ask
Edit:
fair
made a screenshot that can help understand what's the current population versus potential population, due the buildings being made (unfinished ones)
*EDIT*: Screenshot removed on request of fair (the author of the screenshot)