This isn't exactly a bug, it's really a quirk in the quest text.
The first quest is: "Travel to Athens and talk to the Hoplite Leader"
That works as expected.
Then you go to the Messenger of Aristagoras and get the second quest, "Talk to Leader Hoplite and the Dockmaster", but there is no Dockmaster to talk to. You just talk to the Hoplite Leader a second time and complete the quest.
The first two times I did these quests I looked all over Athens, trying to find the Dockmaster, before I realized that the quest was already completed.
The first quest is: "Travel to Athens and talk to the Hoplite Leader"
That works as expected.
Then you go to the Messenger of Aristagoras and get the second quest, "Talk to Leader Hoplite and the Dockmaster", but there is no Dockmaster to talk to. You just talk to the Hoplite Leader a second time and complete the quest.
The first two times I did these quests I looked all over Athens, trying to find the Dockmaster, before I realized that the quest was already completed.