Hi,
the 3th of november, I saw the bug in attachment with the Mine.
I trashed 3 golds and at the end of the action phase, I have only 2 in hand.
From the screenshot you trashed Gold with Mine twice, so the 3 plays of Mine only netted you 1 Gold. (+1 Gold that you drew before presumably.)
Markus is right. At the time you started trashing with Mine, you had a Silver and a Gold in your hand (you had put a Copper somewhere into your deck with Secret Passage previously). Since Mine doesn't change the number of treasures in your hand, you ended up with 2 Gold.