Almost two years ago I published a blog post with a tool that I developed to help debug data merge and layout problems: http://blogs.adobe.com/formfeed/2009/05/debug_merge_and_layout.html
I continue to use this sample pdf on a regular basis. It has a reserved location among my desktop icons for quick access. But occasionally I’d run into PDF forms that cause it to hang. So finally I took the time to find and fix the problem. While I was at it, I took care of a couple other minor issues. The updated form is available for download here. I hope you find it useful.