The synopsis said -D will set the debug level. It doesn't -d sets it, as is stated in the options. SYNOPSIS net {<ads|rap|rpc>} [-h] [-w workgroup] [-W myworkgroup] [-U user] [-I ip-address] [-p port] [-n myname] [-s conffile] [-S server] [-l] [-P] [-D debuglevel] OPTIONS -d|--debuglevel=level level is an integer from 0 to 10. The default value if this pa- rameter is not specified is zero.
committed a patch in samba-docs