ghc 6.2 panic or program segfault, depending on flags

If I compile my program with -O or -O2, I get the following:

[abe@basil:~/local/tla/genome/src/test] $ ghc -O -package genome -o test
test.hs
ghc-6.2: panic! (the `impossible' happened, GHC version 6.2):
        simplCore/Simplify.lhs:1538: Non-exhaustive patterns in function
bind_args

However, if I add -dcore-lint or remove the -O, the program compiles but
segfaults mid-run.  This bug showed up when I added an "Eq a" context to a
typeclass definition in some code in the genome package (which itself
compiles fine with or without optimizations).

In addition, if instead of compiling the genome code as a package, I build
it into the test program using ghc --make, the resulting test program
compiles *and* runs without problems, even with -O.

Unfortunately, as with Isaac Jones, I working with Aetion internal code
and can't post it, but I'll happily do any follow-up investigation people
suggest.

Abe