Thank you for your post.
I was able to replicate the problem on my iMac using FileMaker Pro 11.0v2 on Mac OS X 10.5.8.
It appears the Freeze Window script step, even though should be ignored in Instant Web Publishing, is interfering with the script. Once the Freeze Window script step is disabled, the script works correctly.
I have reported the problem to our Development and Software Quality Assurance (Testing) departments for review.