internal error: evacuate: strange closure type

While running my test and benchmarking program for Etage-Graph package, I am getting sometimes (in around 1% runs) the following error (with different closure type number):

test: internal error: evacuate: strange closure type 4869608
    (GHC version 7.1.20101124 for x86_64_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted

As it is not very often it is hard to debug. I am running the program as:

./test -s 400 +RTS -N4

Where 400 is number of nodes in the graph. Maybe it also happens with smaller number of nodes.

Trac metadata

Trac field	Value
Version	7.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	mmitar@gmail.com
Operating system
Architecture