[racket] How to start embedded racket from a pthread?

Hi,

I started a new application with embedded racket and got the example
listed in "Inside: Racket C API" section 1.4 for 3m up and running.
However, I wish to start racket from a pthread instead of the main
thread, and when I do that the program stops with the following error:

SIGSEGV MAPERR si_code 1 fault on addr 0x8
Aborted

I browsed through the rest of the C API manual looking for hints of
what to adjust but nothing jumped out at me. So, what is the secret to
get this working?

--Pedro