Windows Defender not recording scans properly

Around nine days ago, Windows Defender prompted me to scan my computer because I "haven't scanned (my) computer in 1 day." So I ran a full system scan, after which the Last scan date reflected that I had just scanned my computer.

The next day, Windows Defender prompted me to scan my computer again because I "haven't scanned (my) computer in 2 days." So I ran a full system scan again, after which the Last scan date was again updated.

The day after that, Windows Defender prompted me to scan my computer yet again because I "haven't scanned (my) computer in 3 days." I've been scanning my system every day, alternating between quick scan and full scan but Windows Defender keeps telling me that I have not scanned my computer plus one day. Now Windows Defender tells me I haven't scanned my computer in 9 days, but I just launched a quick scan last night.

What is going on here? :confused

 

I do have CCleaner and I run it two to five times a day after searching for torrents! I'll untick (Is there such a word?) the box for Windows Defender and see if that solves the mystery. :major

I have Windows Vista SP1 installed. The only third party anti-malware program I'm using is Kaspersky Antivirus 2009 and it doesn't detect any malware, just vulnerabilities. And I have Windows Firewall and Windows Defender activated. Plus the built-in firewall of the router.