Fixing problem: validation errors ignored on redirects. Closes #476

In conversation on Issue #476, @lucascs asked me to do this PR to start the bug fix.

Here the gist with the problematic controller as he asked me: [Problematic Controller](https://gist.github.com/renanigt/6f88e6fced50bce47ac9)
Use `java.lang.IllegalStateException` instead