iis logging and isapi filters

a difficult question: i have developed two ISAPI filters and loaded fine
on my Windows 2003 server.
I have user VC++ 6 and MFC.

Both filters use the CHttpFilter::OnLog notification to do something
before the "real" log stars.
Each filter is used on two different sites. Let's say filter1 on site1 and
filter2 on site2.

The problem is that with logging *disabled*, the filter2 "correctly" does
not work (OnLog is not called by the framework) while filter1 works
independently by the logging enabled or disabled in the site's properties
(IIS Management Console).

I would very much like to have the filter2 to work without IIS logging
enabled, but I don't understand how that works with filter1. I have tried
almost anything, please help!

Thanks.