"Run a downgrade 2.6 -> 2.4, with a TIV2 index in place. Expected behavior: 2.4.9 should report the issue and fail inserts, since it checks the index version. Prior to 2.4.9 doesn’t check, so it can cause index corruption if language names aren’t just all lowercase in the existing index entries (cause they can’t be removed by 2.4.<9). "

We need to document this and strongly warn that only downgrading to 2.4.9 should be done, because if the user downgrades to 2.4.8 or lower they could end up corrupting their index.