What you describe sounds a lot like this issue: https://github.com/commercialhaskell/stack/issues/2545

On Wed, Sep 14, 2016 at 1:26 PM David McBride <toad3k@gmail.com> wrote:
That's not what I'm observering.  I intentially put -Wall and some odd code in a local copy of pipes-csv, stack clean, stack build.

/home/toad/working/pipes-csv-1.4.0/src/Pipes/Csv.hs:216:3: Warning:
    A do-notation statement discarded a result of type ‘String’
    Suppress this warning by saying ‘_ <- getLine’
    or by using the flag -fno-warn-unused-do-bind

In another project, stack clean, stack build

pipes-csv-1.4.0: configure
pipes-csv-1.4.0: build
pipes-csv-1.4.0: copy/register

Nothing at all.

stack.yaml is basically this, but with a few extra packages.

flags: {}
packages:
- '.'
- '../pipes-csv-1.4.0'
extra-deps: []
resolver: lts-3.1

stack --version
Version 1.1.2 x86_64 hpack-0.14.0