This has bit me once or twice, and just bit Lukas on Fennec 4.0b5. We respin the mobile release and only land a change on one repo. The other repo's revision stays the same. However, since the revision stays the same, we don't pick up the version bump that happened in build 1. In a way, I prefer having a check over a documentation warning, since it's automatic. On the other hand, I don't like hardcoding an assumption that we don't want to build off the same revision. Not really sure when we would want to not build off the version-bumped revision, if any, though. I could see this potentially being a small edge case in Firefox releases, but it's more common in Fennec releases since there's a higher chance we'll keep one revision the same across 2 repos.
Version bumps are a non-issue in our current release process.