Sparkling mine changed to Mine !

[regpath]

I was about to upgrade my 'Sparkling Mine' from Level 2 to Level 3.
Then I found that it had changed to 'Mine'.
I built another 'Sparkling Mine' and upgraded to Level 2.
Then one day, it again changed to 'Mine'.
What does it happen?
Are they same?

[maguar]

They're the same but they have a shorter collection time. I think it would have been too long to out sparkling mine level x (but that's just my theory). If you read the description (next to the upgrade button) it still calls it a sparkling mine.