The error is:
tapestry.js, line 1462: 'undefined' is null or not an object
This happened in IE8. It's reproducible with and without enabling IE7 compatible mode. A user on the mailing list suggested that he saw similar error messages in his FF console.
I saw this for the forst time after upgrading to Tapestry 5.2.0.
I would expect, Tapestry not interacting with a form in the template, as long as it's plain markup and not a form component.