Some seem to be fixed by now (there was work on buying Mint + other on-buy effects).
With Haggler in play, buy Mint, gaining&playing x, then resolve the Mint trashing. X should be trashed if it's a Treasure, but it stays in play. All the other Treasures are trashed. X could be a Crown, a Capitalism-changed Action, or a normal Treasure played from your hand via gaining&playing Black Market/Storyteller/Crown.
Edit: If you play several Treasures with Black Market, neither of them are trashed. Only the Treasures that were originally in play when you bought the Mint.
This is all fixed now, you can check each case in 36604916.
hat I wanted to test, which is not possible because of the Mint bug, was this:
With Haggler in play, buy Mint, gaining&playing Haggler (cost-reduced), then resolve the Mint trashing. Now the 2nd Haggler, which was not there originally, is not there now anymore either, but it triggered so you should still be able to gain another cheaper card than the Mint.
This also works, game 36605048.