I experienced this earlier, though not entirely sure if this is a bug or if it's intended to be this way.
This is how it happens.
You click your city list, so the drop down appears.
You double click your city name "accidentally" ( as if you mean to change its name ).
The list then closes and opens again, but this time when you click another city ( besides the one currently in the overview ) that city will be renamed to the city you are currently on but this time with a number. The more you do so with that same city name, the higher the number goes.
You probably did this by accident. I know I did.