Well, that's it, exactly. May I ask why you click on (all) the three right-side buttons?
By clicking on all of them, you select the scanning of three areas - removable devices, all local hard disks, and selected area. So, avast! scans your diskette first (which isn't there), then scans your whole disk and then goes on with scanning whatever you selected in the "third button", so it really scans some folders twice.
There's no need to click the first two buttons if you want to select the exact area - use only the third one.