Procmail and Solaris 2.5.1

I compiled procmail on Solaris with a SYSTEM_MBOX of
/var/mail/$LOGNAME.  I'm using procmail with sendmail 8.7.5.

Mail hangs everytime it tries to deliver to a user who has vacation
turned on.  Also, a number of users have complained that mailtool
becomes confused quite often.

Is there a nuance that I'm missing?

-Lewis