POP filters in Kmail

I have set a POP filter in my Kmail (v 1.9.10, under KDE v3.5.10) to catch 
mail from two especially annoying sources of spam that I want to keep out 
of even the trash folder: "Any mail From <contains given address> --> 
Delete from server".

This doesn't work, and mail from those addresses are still being deposited 
in the trash folder (courtesy of another, non-POP, filter).

Do POP filters work, or is this a feature that has not been fully 
implemented? If this should work, why doesn't it? what am I doing wrong?

-- 
Stan Goodman
Qiryat Tiv'on
Israel