Sounds like you are doing nothing wrong.  Each new release of sdb
has a couple more commands that work.  Maybe someday more than
half will. :-)
My favorite is single step 10 instructions:
s10
symbol not found
-- 
Phil Hughes, SSC, Inc. P.O. Box 55549, Seattle, WA 98155  (206)FOR-UNIX
    amc-gw!ssc!fyl or uunet!pilchuck!ssc!fyl or attmail!ssc!fyl