Thanks, Craig! I posted the same question on the forum at robertsrules.com, and after a surprisingly lively discussion, this consensus emerged:
1) The chair can raise a point of order pointing out the ambiguity, and can rule on the point of order.
2) Any challenge to the chair's ruling must be conducted under terms of the chair's ruling. (That is, if the chair's ruling means a certain group cannot vote, that group cannot vote on the challenge.) Any other interpretation leads to circular logic (we cannot vote on who can vote until we've voted on who can vote), and thus to the absurdity that the assembly must be dissolved and reconstituted with the ambiguity resolved before any business can be conducted -- an obviously dilatory result, and it is the chair's *duty* (not just power) to suppress dilatory motions.
Sorry for not posting this here after coming to this consensus in a different forum.
"If a bylaw is ambiguous, it must be interpreted, if possible, in harmony with the other bylaws. The interpretation should be in accordance with the intention of the society at the time the bylaw was adopted, as far as this can be determined."
Robert's Rules also says that if a bylaw is ambiguous and one interpretation would contradict other bylaws and another interpretation wouldn't contradict other bylaws, you must use the interpretation that doesn't contradict other bylaws.
My interpretation of this is simply that you go with the intent of the (by)law rather than the letter of the (by)law.
So I would say yes, the chair can make the determination, but that determination must follow the "intent" rule. And, as always, the chair's ruling is subject to challenge from the floor.
Suppose an ambiguity exists in a bylaw, and even the parliamentarian acknowledges that two conflicting interpretations are possible. Suppose the ambiguity is not discovered until resolving it becomes important during a meeting.
Does the chair have authority to declare which interpretation is operative? If not, what's the proper procedure?
