I have an odd problem with my CiviEvent registration.
When a user fills out a registration form and selects the "Pay later" payment option, on clicking "Continue" the browser throws an "are you sure you want to leave this page" message. (Everything works if the user then clicks "OK", it's just confusing to the user to see a message "you may lose any changes on this page".) If they choose the online payment option and fill out the billing information, "Continue" properly takes them to the next confirmation page.
The only other question I've found that discusses this is
and it seems I can disable the message by manipulating the onbeforeunload JS function (which I will try) but I'd really like to know what the core problem is instead of just putting a band-aid on it :-)
System deets: Joomla 3.8.12, CiviCRM 5.3.1