chatserv writes:  

When a user uploads an avatar through the forums and later decides to change to a new avatar the previously uploaded avatar gets deleted, by mistake Nuke's default profile manager saves any avatar selected from within it without saving to the users database table its avatar_type value, since no type is defined the type gets set to 0 which is the default value, in forum terms any avatar with a type value of 0 or 1 is presumed to have been uploaded and as such it gets marked as deletable even if it is a gallery avatar hence why any avatar gets deleted when a new one is selected through the forum's profile manager.
For my proposed fix go here.