In readProcessWithExitCode, when child dies without reading whole input we get a pipe error. This happens when child program is not satisfied with input or does not need whole input. In such a case error code from the child program is more expected.

The solution is to ignore write error (broken pipe).

For a (short) discussion of issue see thread:

http://www.haskell.org/pipermail/libraries/2010-December/015366.html

Attached patch ignores output exceptions.