emacs-compatible lockfiles

I use procmail (v3.03) to deliver mail to emacs folders, and
as suggested in the man page PROCMAILEX(5) I use emacs-compatible
lockfiles in ~/.procmailrc, eg.

:0:/local/gnu/lib/emacs/lock/!home!stovner!a!ssupport!Mail!error
* ^FROM_MAILER
error

However, this does not work properly, when procmail tries to deliver
to the error-mailbox at the same time as emacs (rmail) is reading, I
end up with to mailboxes:

  error  - which contains just one letter, usually 'F' (the first
           letter of the incoming mail)
  error+ - which contails the rest of the incoming mail.

It looks like procmail is writing one letter to the folder
_before_ locking the file, and when rmail tries to read
the mailbox it gets only the one letter, and of course cannot
convert this to babyl-format.

Any suggestions?

Thanks,

Andreas Sorensen
andreass(_at_)a(_dot_)sn(_dot_)no