This has been the case for a VERY long time mate. It's an extremely minor bug imo, literally only affecting like groups of pve trash mobs when questing.
Too complex for ZoS to care. It is mechanic since beta, all attacks copy passives or proc enchants from active weapon on hit
(anyway interesting calling heavy attack hitting for 68% damage some group ... big deal)
It's not a big deal for some because we have become so used to all that free damage floating around. When thinking about bugs like that you almost say: "Well at least he had to push a button and bar swap for the free damage..."