Are you running the registry section of ccleaner? Does steam use flash cookies or internet explorer dom storage? If you wait a bit, there are quite a few members who use steam including one, @Winapp2.ini who runs our user entry template thread.
Well unmax everything, only clean things from the registry you know you don't need and it's likely (just from the second advice) you won't have this issue.
If you have to use the cleaning section "maxed out" you'll need to run the slow process of
1) check one item
2) run clean
3) Check steam
4) if not broken check the next item and run through 1-3 until the issue occurs.
It also strikes me to confirm that you don't have a winapp2.ini file or use any ccleaner "enhancing" items.