Guild Wars 2

If you are supposed to get knock back or stopped from gathering (with the correct tool) and you do not (for examble you are supposed to get knocked back from a worm’s attack and you are a warrior with the Last Stand trait) your gathering is ruined.

This also reliably happens with Superior Rune of the Pirate when proccing the “5% chance to shout Yarr and grant Might to nearby allies when hit.”

It’s a known bug. If I recall it happens any time something (trait, rune, etc.) activates while gathering/harvesting.