Is it a bug? Yes, NoWorkDupe No Work.

[Robert A. Wilson]

Yes, it is a bug (I reported it to K1EA via FAX about 6 months ago).
NOWORKDUPE "no work" if you use typeahead.

There is also another unfortunte scenario.  Suppose you have already
worked Lloyd, AA6T.  Then Bill, AA6TT calls you.  You press

   A  A  6  T  <INSert>  T

and CT sends "QSO B4" even though AA6TT is not a dupe!  I really
hope Ken can fix this some day.  It is nice to know I'm not the only one
who has been frustrated by this problem.  Unless it was fixed recently,
I think the bug is still there.

One possible option would be for CT to <wait> until you move the cursor
out of the callsign field before it activates the "INSert" function
(sending callsign and exchange).  It might make the CW hesitate for
a moment if you are a really slow typist, but this should be acceptable.

73,
Bob, N6TV