mutt -p failed to send message, how to fix?

[Paul Drynoff <pauldrynoff@xxxxxxxxx>]

Hello.

I have something like this in ~/.muttrc
set sendmail = "/usr/bin/nbsmtp ..."

and can successfully send message,
but if I postpone email, and after that 
start mutt with "-p" option, on attempt send mail it tell
something like this:
sendmail: invalid option -- o                                                   
                      
Usage: sendmail -f from@xxxxxxxxxxx -h relayhost [OPTIONS] (use -H for help)

why mutt tries to use "-o" option and how force him to not use this 
strange option?