Donatello skill does not work.

Hey Guys,

I do have donatello in 1 city and when I activate the skill to get free finishing on buildings (currently lvl 7, so 50% free finishing), it does not work... It does not matter how much a building has left, that never lets me finish it for free when the skill is activated.
Am I missing anything? I do have Donatello at 1 city.

Thanks,

Mallor