I've created a patch for this issue #4663 Problem with prototype UJS and pictures as links - Ruby on Rails - rails.
As explained in the comments, this issue doesn't occur with github.com/ rails/prototype-ujs as this requires prototype 1.7 rc2 and this version handles event delegation better than prototype 1.6.
So I've only change the rails.js file in the rails master branch.
Hope I could help.
C+++
