Alan,

Why not just gracefully close the sql*plus session? It will close all
cursors (even those that are associated with recursive sql) and tracing
will be turned off as there is nothing to trace if the session does not
exist anymore.

I just ran a test on 9206 on WinXP and I get execution plans for my
UPDATEs, with or without predicates or subqueries. You might be hitting
a bug. I know that earlier versions (9.2.0.3 and earlier including 8i)
had a bug where STAT lines were not emitted for some queries (I found
it in queries executed as part of logon triggers). You might be hitting
a bug.

Dan