Hello,
I have the same incorrect behaviour at my site with the same versions of Joomla and JEvents as above.
After changing a custom layout and saving, there is no easy way to get back the former layout code. But I found out a workaround, hoping that this issue is soon be fixed:
I restored my side from a recent backup and changed the code of the custom layout at the relevant database-field in the table …jev_defaults. This works, but shout only be a makeshift solution.
Greetings
Miba