How to reproduce:

• Create a valid maillist with an arbitrary name, so that the list is the last in the list of maillists
• Edit the maillist and change its name somehow (e. g. add X at the end of the name)
• Save the edited maillist

Instead of changing name, the maillist will disappear permanently.

The cause is in ui/edit_maillists.lua:62 - a maillist is deleted after it's updated (mail.update_maillist() already removes the old list entry).