Mining

Well, i'm playing right now on an P-Server and i'm totally confused...

Everyone says that Droprates like from Thief's Glove or
20% Chance on Double Item drop has an effect on Mining.

Is that in any way even true?
Can someone eventually explain that detailed?

The default Thief's Glove and Double item have no effect to mining. Maybe on that Server you play, they changed it and they affect mining.