• Steps to reproduce :
  • Create an url activity with https://moodle.org/?foo=a&foo=b as target url
  • Open the link activity
• What happens :
  • The url https://moodle.org/?foo=b is opened (notice that foo=a have been droped) 
• What should happens :
  • The url https://moodle.org/?foo=a&foo=b should be opened

Url with multiple parameters with the same name might be strange, but they exist. For example, you get these url with you have a GET form with a select form element with the multiple attribute.

Page to url that use multiple parameters with same name get broken when linked with the URL activity (the bug doesn't happen if we do a link in the text editor, the bug is specific to the url activity).

The url activity give us the abbility to add URL variable. This is probably the source of the problem.