If the Location or URL field or the Event Image “field” changes, any data that was entered in to any of the Custom Fields will be cleared.
This feels like a bug rather than intended behavior. If it is a bug..
This is happening on a up to date version of Discourse, v2026.8.0-latest.1 +274, on the default theme, across browsers / computers / users.
I am unable to test it on try.discourse.org as there aren’t any custom fields enabled there but if someone wants to enable one I will happily confirm it there.
Here is a video of the behavior for the location field but it would behave exactly the same if I uploaded an image.