The message you're getting about event.returnValue is a warning, it shouldn't be causing your problem. This is basic, but you didn't show your gemfile, I'm assuming you have the gem 'jquery-rails' listed. Also, it should be a relatively current version as the older versions had an issue with this. Finally, if there are any jquery files in your assets/javascripts folder, you should delete them. I'm covering these bases only because it sounds like you had an older app that was working and were forced to update it.
Other than that, I would follow Hassan's recommendation and rebuild. Links are not really intended to be used to pass a post, so Rails has basically rigged it by using javascript to generate a form and submit it. IMO, it's not a great architecture. If javascript is disabled or there are errors, it defaults to sending it as a get. You may want to consider using button_to instead of link_to, or you could also change your route to "match 'withdraw', via: [:get, :post]" to catch both actions.