Create a select list (bug occurs also with other field types) custom field with name FieldName1. Configure the created custom field (e.g. define an Option1 and Option2). Go back to the Custum Fields page. Via the Edit link of the FieldName1 custom field, change the name to FieldName2. Go back to the custom field configure page. Notice the top pane shows as title "Configure Custom Field: FieldName*2*", the bottom pane shows as title "Default Configuration Scheme for FieldName*1*" which is the original name.
Retested on Feb 13th 2008 with 3.6-#153 and 3.12.1-#299, both releases show the bug.