[Haskell-cafe] "cabal sdist" oddity

Cabal from HEAD started to issue the warning "Warning: Cannot run preprocessors. Run 'configure' command first." when running "cabal sdist" after a "cabal install", see e.g. https://travis-ci.org/haskell-opengl/OpenGL/jobs/74581138#L264. Previous versions didn't do this, see e.g. https://travis-ci.org/haskell-opengl/OpenGL/jobs/74581137#L264. Somehow the warning doesn't make sense, because the package has obviously been built before, so configuration must have happened, too. Is this a new bug in Cabal? Cheers, S.