There's a core feature in Admin -> Smileys and Message Icons that lets you "Enable customized message icons". When checked, you can "Edit Message Icons", here you can edit default icons or add new ones. It seems that if custom icons are configured, the checkbox to enable/disable has no effect, custom icons remain either way. Is that how it's supposed to work?
well you have added to the list, I don't see why the icons would get removed just because you stopped customizing them.
Ok, so it doesn't allow you to switch between custom and default icon sets. Where are they in the database? Searching custom filenames comes up empty.