template history

This is odd, when I revert my template to the base version, the template history disappears. (Good.) But then when I paste in my new version and click save then view history, for some reason a huge change log appears. Not sure what's going on, previous templates didn't do this, it would just...

Okay, so I know there's an option that controls how long the template history remains, but is there a rebuild or something I could run to clear it on a manual level?