Tear down copper mine doesn't give back my building licence

[Bihanali]

As mentioned on title. I tried to refresh page, log out then login, but unfortunately my building licence is same.
When i tear down an EXHAUSTED mine, it doesn't give back my building licence.

[Dappadon]

Exhausted mines do not give the licence back when demolished. the licence is returned when the mine initially collapses.

[Bihanali]

can you explain it please? i did not udnerstand with the words "initially collapses".

[Dappadon]

When the mine runs out of copper ore it collapses (falls down) when this happens the licence is given back.

[Bihanali]

understand, thanks