spamword filter: spamword not in mail

[Rein]

I got a lot of spam which was classified as infected by my internet security program (F-secure), which was not detected by Spamihilator. The mail was cleaned with F-secure but let through by Spamihilator. That was quite annoying. I had to remove it each time by hand.
The mail got a extra label in the title being infected: [Schadelijke e-mail verwijderd] (dutch: invected mail removed).

I made this a spamword in the spamword filter.
That worked great.

But: a lot of mail, especially mail from my partners, now receives that spam-flag, while the spamword in question is not found in the mail at all. Not even in the header, or encoded.
But spamwordfilter says it IS found.

How can that be?

[Chactory]

Hallo Rein!

Very interesting question.
Example (screenshots and header)?

Gruß,
Chactory

[Rein]

Hi Chactory!

I's a bit too long ago for a screenshot.
I found another way to get mails like this to be marked as spam:
Copied a part of the standard text (a bit like: this mail was send to you because of....)
That worked too and had no side effects

Regards,
Rein

[Chactory]

Hello Rein!

Thank you for your answer!
That's very good!

Sincerely,
Chactory