dialog box error during compile

[harry]

I was recently having some trouble building a package through an IDE. When I
tried it from the command line, GHC popped up the following dialogue box:

ghc.exe - Entry Point Not Found
The procedure entry point deflateSetHeader could not be located in the
dynamic link library zlib1.dll.

I fixed the error, but I hadn't seen it earlier because the IDE (EclpiseFP)
only gave GHC a console, where the error wasn't written. Why wasn't it
written to the error stream like any other error?

Haskell Platform 2013.2 on Windows. The error occurred when building an
application that uses gtk2hs.