Trident damage bug

Sometimes the damage goes away from the Trident. When I've killed some mobs and I'm going to smash grass, for example, there is no longer any damage on the Trident after I've done it for a while.

Because I can not upload it here, I put it on youtube:
https://www.youtube.com/watch?time_continue=4&v=Xr_wiowwscY