When clicking "Reply" on a discussion post, this script adds a hidden input to mark which post we are replying to.
This cause problem  when ctrl+clicking reply to reply in a new tab, because it leaves the page with the extra hidden input, which cause problems, like clicking reply again cause `Error Value: You are not allowed to access '['1', '1']`' in this context , or clicking change page will reply.

This is a minimal effort fix, just remove the added element after click.

/reviewed-on nexedi/erp5!823