When a ticket is created and the request type is chosen the custom fields appear which is good, however if you start typing in the Request Detail field and then think oh dear I got the wrong Request Type the Custom fields do not disappear when the request type is changed anymore
Any ideas why?
Because the UI isn't capable of it. You'll notice they do disappear once you save the ticket, though. Occasionally it bugs out and you have to leave the ticket and come back to it, or if it's really bad, logout, clear your browser caches, and then restart the browser to try again.