Mr. Magnetta had been elected Council President by vote of the Council on January 3, 2006. As far as I know, no one has challenged the validity of that election. Can the Council change its mind about which member should be its President? Absolutely. But it is my opinion that such an action is in the nature of a motion to amend something previously adopted.
This may seem like a minor parliamentary point, but under Robert's Rules of Order a motion to amend something previously adopted requires a simple majority vote with notice, or a 2/3 vote without notice.
Why does this matter? The agenda for the meeting did not give notice that the Council would vote on "ousting" its President. Only four members of the Council knew that such a motion might be made at that meeting. The other three were taken by surprise, as was the public.
If the council members who wanted to accomplish the removal of their President had been willing to let it be known in advance that such a motion would be made, four votes would have been sufficient.On the other hand, if a 2/3 vote was required to remove an officer without notice, then the motion should have been declared to have failed under the circumstances in which it was made and voted. A 2/3 vote of seven council members should have required five votes to pass.
This is just another consequence of trying to govern by secrecy and surprise.