strictness of interpreted haskell implementations

[Geraint Jones]

Are there well-known differences in the implementations of Haskell in
ghci and hugs?  I've got some moderately intricate code (simulations
of pipelined processors) that behave differently - apparently because
ghci Haskell is stricter than hugs Haskell, and I cannot find any 
obviously relevant claims about strictness in the documentation.