[plt-scheme] optimizer crash in embedded mzscheme

Hi all,

I've upgraded from 3.99 to 4.1 and I've started getting crashes in my
mzscheme embedded app. They're coming from errors in my scheme module
code, which are being correctly reported by the optimiser, but crashes
in scheme_log_message. 

This only seems to be happening after I've reset my interpreter by
calling scheme_basic_env() a second time - which may or may not be
related.

Just thought I'd ask before delving deeper in case it's a simple API
change I've missed. I'll try and cobble together some smallish amount of
code that exhibits this if it's required.

cheers,

dave