With regret, I deregister. My planned reasoning for CFJ 3436, in summary: in the past, we have generally considered one phrase to be a synonym of another if the latter phrase clearly matches the intended meaning of the former phrase. In this case, the intended meaning of "Proposal:" is clearly "I submit the following document as a proposal", and so the former word is a synonym of the latter phrase, and therefore is effective.
Examples of synonyms we have allowed in the past, in support of the above: conditional statements as synonyms for their consequents, if their antecedents are true (which is the only mechanism by which conditional statements work correctly); misspellings as synonyms; synonyms defined on the spot (CFJ 1361); scshunt's vote of "SURE WHY NOT" on Proposal 7451. I note that Proposal 7614, passed this January, removed the clause in the rules by which synonyms are considered interchangeable. RIP 1993–2014. —the Warrigal