Iface type variable out of scope: s

I just tried to install criterion with the current GHC HEAD, and statistics failed with this message:

/home/jojo/.cabal/lib/x86_64-linux-ghc-7.9.20140609/math-functions-0.1.5.2/Numeric/Sum.hi
Declaration for R:MVectorsKBNSum:
  Iface type variable out of scope:  s
Cannot continue after interface file error

I tried to reproduce this with smaller code than statistics, but could not trigger it.

The interface dump gives me:

661d69e55c1491128ac1ed3c03f864e2
  axiom TFCo:R:MVectorsKB2Sum::
      Data.Vector.Unboxed.Base.MVector s0 Numeric.Sum.KB2Sum
        = Numeric.Sum.R:MVectorsKB2Sum s0
a69bb56c3760003bcb7d99cd40c3d843
  axiom TFCo:R:MVectorsKBNSum::
      Data.Vector.Unboxed.Base.MVector s0 Numeric.Sum.KBNSum
        = Numeric.Sum.R:MVectorsKBNSum s0

– not sure if there is a forall missing or note. Note that these data types are generated using template haskell source.

In order to reproduce this, run someting like cabal install --with-compiler=.../inplace/bin/ghc-stage2 --ghc-option=-XTypeFamilies . in statistics-0.11.0.3 with the attached patch applied.