Weapon firing desyncs if holding fire button on spawn
In online, if you hold the fire button as you spawn/respawn, your shots come out before the firing animation plays. The time difference between the shot coming out due to the desync and the shot being supposed to come out under normal circumstances is proportional to the player's ping, so it's most easily noticeable if the player has a high ping to the server. The desync goes away once the player lets go of the fire button.
Might be worth noting that other ports like ZDaemon and Skulltag/Zandronum also had this same issue in the past, but Zandronum has since corrected this bug, and my guess is that ZDaemon works around this bug by temporarily disabling unlagged for shots like this, so they still come out where the player's aim is intended.
I notice this a lot with the BFG on maps like Judas23 that have starts that give it to you