I haven't used JIRA recently, but as far as I remember the difference existed because they were rolling out a "new" editor, which was active when editing ticket

I haven't used JIRA recently, but as far as I remember the difference existed because they were rolling out a "new" editor, which was active when editing tickets, but wasn't available when creating new ones. I remember this caused me some data corruption when editing a comment created with the old version of the editor using the new editor. It was a mess.