[Dovecot] question mailbox format

[sc2 at gmx.at]

i set mail_location = mbox:/var/spool/mail/%u
and protocols = pop3s pop3
why he trys to create and use imap format?`

in log are
May 25 18:52:25 mail dovecot: pop3-login: Login: user=<richard>, 
method=PLAIN,
rip=80.xx.xx.xx, lip=xx.xx.24.29, TLS
May 25 18:52:26 mail dovecot: POP3(richard): 
open(/var/spool/mail/richard/inbo
x, O_CREAT) failed: Not a directory
May 25 18:52:26 mail dovecot: POP3(richard): 
mkdir_parents(/var/spool/mail/richard/.imap/INBOX) failed: Not a directory
May 25 18:52:26 mail dovecot: POP3(richard): stat() failed with mbox file 
/var/
spool/mail/richard/inbox: Not a directory
May 25 18:52:26 mail dovecot: POP3(richard): Couldn't init INBOX: Internal 
erro
r occurred. Refer to server log for more information. [2007-05-25 18:52:25]
May 25 18:52:26 mail dovecot: POP3(richard): Mailbox init failed top=0/0, 
retr=
0/0, del=0/0, size=0

friendly regards and thx