Precompiler LOCK TABLE doesn't work

I have a PROFORTRAN application, under ORACLE 7.0.16.6.2, that does the following:

EXEC SQL LOCK TABLE FRED IN EXCLUSIVE MODE There is no COMMIT, the code goes to sleep (but keeps running... it does NOT terminate) after this...
There are no errors...

but...

the table isn't locked. I can still update/insert/delete from SQLPLUS in another window.

This works if I issue the lock right at a SQLPLUS prompt.

What's the problem?

Yes, I have called ORACLE support. They are scratching their heads and looking at my code and I don't expect to hear from them any time soon, except what they already told me... "Gee, that SHOULD work..."

So, if anyone has experienced this problem, please tell me what I am doing wrong.

-- 
Max Magliaro
MMM_at_ICF.HRB.COM
Philipsburg, Pennsylvania

"He may look like an idiot, and he may sound like an idiot, but don't
 let him fool you.  He really is an idiot." --- Groucho Marx