Fresh install of GCC 4.6.0, error with Boost Serialization

[doug livesey <biot023 at gmail dot com>]

Hi -- I've installed GCC 4.6.0 on my MacBook Pro (running Snow
Leopard), and have compiled a simple hello world c++ program with it.
Unfortunately, when I try to do something more complex using the Boost
Serialization library, the code compiles and links, but I get the
following error when I run it:
?? run_features(2872) malloc: *** error for object 0x100502060:
pointer being freed was not allocated
?? *** set a breakpoint in malloc_error_break to debug

This occurs when I try to create an xml archive with a stringstream.
The code compiles fine under GCC 4.2, it's only with 4.6.0 that I get
this error. I reinstalled Boost with GCC 4.6.0 (by fixing symlinks to
cc, gcc, and g++ & using homebrew) to be sure that it wasn't something
there.
For reference, the error is caused by line 24 of this file:
https://gist.github.com/923262
I'm just learning C++ & GCC development, so I'm a bit stumped, now, as
to what I can do next -- could anyone advise me on how I might resolve
this, or where I might look for information to help me?
Thanks very much,
?? Doug.