I have some basic HTML in an event's "Complete Description" - a link to an image, and a change to the style of some text. This works fine. When I try and do the same on the "Introductory Text" of the registration screen and then click "Save", screen seems to freeze with spinny cursor. I then have to go backwards in browser to return to responsive CiviCRM. Re-visiting the event, "Introductory Text" is as it was before edit. I can save with basic text, and add simple HTML such as a bold tag but as soon as I add the image, it doesn't save. Version is 5.18.