weird activation record found on stack

Hello.

I got this one off. The rest of the time this program gives a simple 
Segmentation Fault near startup (about 1 in 5 times), and the other 4 in 5 
times runs through to completion.

$ ~/src/haskellgitmaildir/a.out master mundungusmaster
base=aeb5d7eb11acbb81d77f37d381b75a51a8897eb9
a.out: internal error: scavenge_stack: weird activation record found on 
stack: 59
    Please report this as a bug to glasgow-haskell-bugs@xxxxxxxxxxx,
    or http://www.sourceforge.net/projects/ghc/
piva:~/tmp/littlemaildir benc$


For my reference, the version of the code that produces this is commit 
9c3e10ea248b1391851ac0d7f8e15f3b0939ec01.

Possibly of relevance, I'm doing some forkIO and running processes.

piva:~/tmp/littlemaildir benc$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.4.1

piva:~/tmp/littlemaildir benc$ uname -a
Darwin piva.hawaga.org.uk 8.3.0 Darwin Kernel Version 8.3.0: Mon Oct  3 
20:04:04 PDT 2005; root:xnu-792.6.22.obj~2/RELEASE_PPC Power Macintosh 
powerpc

What other info do you want?

Ben
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