[plt-scheme] Using threads in Teaching Languages through teachpack

I posted this general issue last week but I've narrowed it down just a 
bit.  I still need your help.  The goal is to give students a teachpack 
that lets them create threads.  This simple teachpack works fine in 
"Textual" but fails in "Advanced Student" (v300 and v301).  Here is the 
teachpack:

(module exposethread mzscheme
  (provide thread)
  )

and here is the error from evaluating (thread (lambda () (display "show 
this independently")))

hash-table-get: expects type <hash-table> as 1st argument, given: false; 
other arguments were: 'test-coverage-point22886

Maybe I'm missing something simple?  As I mentioned before, this works 
fine in v207. Thanks in advance,
--Wayne Iba