This is not a big issue compared to the stability, performance and features of the next kde release.

The tooltip of the digital clock on the plasma bar will show the time in different timezones (cities). Which cities to show on the tooltip can be configured in the timezone settings of the digital clock.

Since 4.8beta the digital clock automatically shows the capital city of my location on the tooltip. So if my location is The Netherlands, the city Amsterdam will automatically be shown on the tooltip.

This is practical for most people, but I prefer to choose the cities myself. It would be nice if the user can unselect this city in the timezone settings.

You are still able to do this. Open the clock settings, and use the Timezone tab to select the appropriate City / Timezone you need.

Yes, I can select other cities, but I cannot unselect the city that was automatically chosen.

Edit:
Ah, now I understand your answer
You mean the settings for Date & Time (in System Settings) and not the settings of the Plasma Clock.

Thanks, it works.

Good to see you found the answer (even though I hadn't thought of checking there to see if a City option had been added in System Settings > Date & Time)