Summary: I have a manager "Alan". "Bob" is not my manager but during meetings he often gives me tasks and talks about his participation in my work. I feel uncomfortable but my manager doesn't know what to do.
I have a weekly meeting during which I've been asked to just listen in for situational awareness. The project leader, "Alan," keeps it short and simple. I regularly report on my progress to Alan at a separate meeting, plus whenever I'm asked by him to do so.
During the last several meetings, someone else involved in the project (call them "Bob"), who is neither the project lead, nor someone I report to, calls on me to discuss my efforts during the past week. He'll then jump in to discuss how he's supporting my work (which he's not, so it is a total lie) and then creates tasks assigns me tasks in front of everyone, giving him the appearance of being my supervisor.
This is not the first time Bob has done this. Two former project teammates had this happen to them (on other projects), and they didn't like it either. The first one left for unrelated reasons, and the second left the project due to Bob's behavior in general. Bob likes to make himself look like he's in charge, insinuate himself into situations, put himself between people's lines of communication to control projects and make himself the hub of everything. Bob has even tried to get between Alan and our customer. Bob's boss "Charlie", meanwhile, gives Bob a very long leash because Bob lets Charlie take credit, so Charlie is happy. Charlie is not my supervisor, nor Alan's.
I've talked to Alan, and while he understands and agrees, he's at a loss for what to do. I have a few ideas, and would prefer to stay on the project, but I don't want to make an uncomfortable situation worse.
How do you manage someone who passive-aggressively gets between people, makes themselves appear to be in charge, and lies/bullies to do it?
EDIT: The main difference here compared to another question is that in this case, the issue of third parties being present and involved further complicates the issue.