Custom spam scanner score not getting added

[ram]

I have MailScanner 4.64 on my servers where I see that sometimes the
score given by is not added to the total score while marking a mail
spam 


So if SpamAssassin returns 0 score and Custom Scanner returns 7 the mail
should be marked as spam. In most cases this works but some mails
strangely enough dont get marked spam 

It happens rarely , 3-4 times in a day ,  and is not replicated , so I
dont now how do I check this 

Any pointers ?? 


Thanks
Ram