A question about MSSE

[Delta Echo]

Does Microsoft Security Essentials quick-scan different numbers of files at different times based on computer useage or something? I got a new computer last week (yay!) and have noticed that, over time, it seems to scan fewer files whenever the quick-scan is run (usually run it once a day). Normally around 180,000 something files (I think), but this evening I decided to run a full scan (since I hadn't previously). I stopped it after about 10 minutes because it was taking awhile, deciding to run it later, and ran a quick-scan, but now it only scanned 12,800 some-odd files.  :o Is that normal?

Also, I noticed it seems to scan wmplayer.exe several times torwards the end (it was doing that before, too) and that's the last file it scans before stopping and saying it's complete. Is that also normal?

A full scan using MBAM turned up nothing, so I don't think there's anything (and there shouldn't be), I'm just curious...