Despite claims from an arenanet game designer posting on the forum, the mystic forge is indeed suffering from (unintended?) diminishing returns.
Since the game designer in question claimed that the mystic forge is not intended to suffer from diminishing returns, this has to be a bug of some kind in the game programming.
Large scale testing has shown this bug is easily reproducible.
All you need to do is stock up on a few stacks of T5 fine crafting materials and T5 dust, and have some spare skillpoints.
Put the T5 fine material, the same material of T6, dust, and philosophers stones in the mystic forge, and confirm you want to forge them.
Now repeat this process 20 times.
You will notice a clear downward pattern in the return of T6 fine materials, until you eventually no longer get more than the bare minimum possible crafting materials from the conversion.
Now get 50 of your friends or guild mates to test this as well. They will all get exactly the same results.
This doesn’t only apply to fine crafting materials, it applies to EVERYTHING that involves a random element in the mystic forge. Including making exotics using rare equipment, or using exotic weapons to make a legendary base weapon. everything is affected by these diminishing returns
