Your two examples make it obvious that question editing should reset the results, but I can imagine less dramatic changes to a question where you not want to reset the results.
For example, if choice #2 had been misspelled as "Oatmael" in the original version of the voite and then corrected by an edit, the previously collected votes would not necessarily have to be deleted.
Since you describe this as a voting system, the behavior of resetting/discarding previous answers whenever a question is edited, can be used to skew the results. For example, if most of the conservatives in an area vote in the morning on their way to work, then editing the question at around 10am could sku the results to the liberal side.
But not resetting previous answers when a question is edited is just as damaging to the validity of the results. If the meaning of the available choices is amended or rearranged, votes collected prior to the change could have their intended meaning modified without the voter's consent.
From a UX point of view, the only appropriate design is to lock the question and choice list as soon as the first vote is cast. Allow editing of up to that moment to allow for spelling corrections and the reordering of choices. Then once the first vote is cast, out of respect for the sanctity of that vote, forbid all further editing.
From a System Design point of view, I can imagine a different option, but it would have to be handled by the database design. The system could allow editing to occur after voting has begun, but it would have to maintain a strict audit of such behavior with enough detail to analyze the entire process after voting is closed.
Every edit of a question or its choice list must be treated as the
creation of a new version.
Every version must to be stored seperately, along with the votes
which were collected for that version.
Final reporting of results must include tallied results for each
version of the question, followed by a tallying of the sum of all
With that much information stored and reportable, and in the absence of summarizing reports which could be used to obscure the stored information, a voting system could exist which would allow for editing of the questions and their choice lists, without compromising the integrity of pre-change votes.