Do you mean it installs the old versions when you install them, or they are re-installing by themselves?
If you've downloaded them before iOS 7, deleted them, and installed later on iOS 7, it would download the iOS 6 versions from iCloud. You can just update them to the new versions.
If they re-installed by themselves, I have no idea. Maybe it has something to do with automatic downloads? Did you install the apps on another device which could have triggered re-download of the apps from iCloud?