Twice since avast 7 was released I have changed the installed components.
The first time (initial release) was to remove remote assistance.
The second time (current version) was to uninstall and reinstall safezone.
Both times this resulted in webshield and mailshield stopping scanning, but with no warning to the user that they were ineffective.
The cause as far as I can tell is that changing components pulls in an additional faulty redirect driver aswRdr.sys (there should only be asw Rdr2.sys I think).
So this seems to be an installer problem - and one that I think was flagged on the initial release of avast 7, but is still there.