Problem with procmail v3.11pre7 1997/04/28

Hello,

I've problems with procmail v3.11pre7 1997/04/28 which I've installed under 
Solaris 2.5 in my personal directory structure right now. Filtering with 
test filters works quite well, but if a new mail does not match the filters 
/var/mail/InBox keeps locked (/var/mail/InBox.lock) and the message will not 
be appended to this InBox immediately. Does anybody know of this sort of 
problem ? Any help and hints is appreciated. 

Regards, Aniello Calcagno.