"Accept bug" has the same effect as "Assign bug to owner of selected component", rather than assigning it to the person doing it. I guess that's a bug, not a feature...
No, it basically changes the status to ASSIGNED and leaves the owner of the bug to whatever currently is set to. If you want to reassign the bug to yourself then you need to enter your email address in the 'Assign bug to _______' field and commit the change. Accept bug (which admittedly may not be clear as to what it means) is basically there to say that it is highly possible that this really is a bug or has actually be verified.