depending on how you set Avast to behave, this can be normal.
What particular behavioural setup did you have in mind Eddy?
They are both configured pretty much the same (except work uses the Network guard - small office), and at work their version was updated to 4.5, while mine was installed @ v4.5.
I only mention it because the PC with the dupe files, is experiencing some problems - freezing when in use etc, and having to be rebooted. Also, all the versions that have been updated online seem to be slow in showing the summary after updating - small thing i know.
So would a clean install help?