Undocumented db_version 26692 solves backend running slow issue

I have had issues on every major upgrade when the db_version changes because i have had to do this manually. It is probably how my webserver/mySQL server are setup, but recently, i started experiencing very slow backend again.

The database version of all my subsites were at the standard 26691, but i found that the database version of my main site was at 26692. Strange, because it is not documented anywhere. I thought it was a mistake and reverted it back to 26691 and it brought the backend down to the bees-knees. Once i changed all my subsites to 26692, the backend is now functioning properly. This is not documented in the Codex.

Has anyone had similar issues at all ?