RTS assertion failure when heap profiling threaded programs.

This is when trying to profile the !QuickHull DPH benchmark. Without -debug we get assertion failures in the RTS heapCensus function. This is on OSX / x86, not sure if it's platform specific.

limitingfactor:dph-examples benl$ pwd
/Users/benl/devel/ghc/build/nightly/ghc-head/libraries/dph/dph-examples

limitingfactor:dph-examples benl$ ../../../inplace/bin/ghc-stage2 -Odph --make spectral/QuickHull/dph/Main.hs  \
  -package dph-prim-par -package dph-par -ispectral/QuickHull/dph \
  -ilib -ispectral/QuickHull/lib -rtsopts -threaded -debug -fforce-recomp

limitingfactor:dph-examples benl$ spectral/QuickHull/dph/Main 1000000 +RTS -DS -N4 -hT       
Main: internal error: ASSERTION FAILED: file rts/sm/Storage.c, line 640

    (GHC version 7.1.20101208 for i386_apple_darwin)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Abort trap

Trac metadata

Trac field	Value
Version	7.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
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Operating system	Unknown/Multiple
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