MLton broken FFI on AMD64???

It  seems that either there is a new bug in the foreign function calling
sequence or something has changed.

I'm using the version of MLton in Debian testing:
    MLton 20100608 (built Tue Jun 15 01:10:03 UTC 2010 on barber)
on a Linux AMD64 architecture.

The following program segfaults when run:

    val printf = _import "printf": string * int -> unit;
    val () = printf ("You are a dog %d0000", 99)
    val () = printf ("Hello silly %d0000", 123)

It prints out the first line but then segfaults on the  second  call  to
printf.

I looked in
    /usr/share/doc/mlton/guide/CallingFromSMLToC
page  and  what  I'm  doing  looks  like it is following the description
there.


On Linux i386, this code works both using the Debian stable  version  of
MLton:
    MLton 20070826 (built Mon Sep 03 18:05:04 2007 on eponym)
and also a version I just built from the repository:
    MLton rexported (built Tue Feb  1 23:22:44 CST 2011 on jupiter)

I  thought  perhaps  it  was  something involving int vs. Int64.int, but
changing the printf type in the ML code to Int64.int made no  difference
on the AMD64 machine.

Any suggestions?