"cabal install" has different working dir. than "cabal build"? (code in TH splice does not/does find data file)

(not sure about the "bug" status but at least it's confusing)

I have a yesod project, using persistent. I am getting this error https://github.com/yesodweb/persistent/issues/633 on `cabal install` BUT compilation succeeds with `cabal build`.

(my sources: but this is a standard yesod setup)

```
$ cabal --version
cabal-install version 3.14.1.1
compiled using version 3.14.1.1 of the Cabal library
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.12.2
```