Inaccessible fields in records

A bit more [indirectly] regarding m开发者_JS百科y previous question: there, my definition of lens was

data Iso α β = Iso { fw :: α -> β, bw :: β -> α }
data Lens α β = forall r. Lens (Iso α (β, r))

And this is fine, as long as the module is imported unqualified. Problems begin with the case where it is, and, for import qualified Util.Lens as L, I get an error about fw not being a (visible) field of constructor Iso. The code itself is trivial,

data BValue = BValue { p :: Float, d :: Float, q :: Float } deriving Show
pLens :: L.Lens BValue Float
pLens = L.Lens (L.Iso { fw = pFwd, bw = pBwd })

The Util.Lens exports both Lens(..) and Iso(..). TIA.

The record fields need to be qualified as well, i.e.:

L.Iso { L.fw = pFwd, L.bw = pBwd }