There is a regression in stack that stack build myexe no longer builds just the executable myexe, but all executables from the package.

Especially projects with many executables, and projects where linking takes a long time suffer from this (both are the case for IOHK's cardano-sl).

The reason according to @mgsloan:

I think this was the result of switching from using runhaskell Setup.hs install to copy + register - f71a515 .
copy fails if it can't find every executable, and there's no way in released cabal to tell it to only copy particular targets. There was a patch well before the most recent cabal release, but for some reason it is only available on master. So, with future cabal this may be fixable.