[plt-scheme] Debugging Multiple Modules

Hi,

My project now consists of around 5 modules each defined in a separate  
file and requiring other modules as necessary.  I define my modules as:

(module my_project_module mzscheme
...
)

and use it with:

(require "my_project_module.scm")

My problem is that I can't seem to debug dependency modules using  
DrScheme.  In other words, I start debugging the top-level module, but  
then DrScheme doesn't seem to trace down through the functions defined in  
other modules.  If they are all defined in one file, then it works, but  
the project is large enough that that is very tedious.  I'm using the  
Pretty Big language, although I've briefly tried a few of the others  
(including module...).

Thanks for any help!

fv