Windows 7: Port scanning with untrue results

Hi people! This is my first post in this forum. Nice to meet yoou =)

I have some very rare issue, I don't know if it is common. The thing is that when I port scan any machine from windows 7 with nmap, free ip tools, etc, it tells me that
there are some ports open that actually aren't open. For e.g., one computer I have at home has 21 and 3603 ports open, and the portscan results says the following:

21/tcp open ftp
22/tcp open ssh
25/tcp open smtp
110/tcp open pop3
119/tcp open nntp
143/tcp open imap
465/tcp open smtps
563/tcp open snews
587/tcp open submission
993/tcp open imaps
995/tcp open pop3s
3306/tcp open mysql


The funny thing is that the exact same other ports shown there, are shown in any scan to any computer I run from windows 7.

I assume that it is not a problem of the port scanning software itself as it happens with any software of its kind. Something to do with winpcap??



I appreciate any suggestion

Regards!