A potential other option..two fields: First known buggy version: Last tested version:
(not necessarily a fan of it, just brainstorming)
I don't think there's a need for a compromise that makes it even more complicated. If we're not going to change the policy, making the version field write-once for most users is fine for enforcing it imo, and as long as we have the original reported version I don't think it's worth adding a field for the last tested one.