Duplicate html id when "Add another item" #ahah is used

I was using a module and noticed a strange behavior when it came to multiple (unlimited) content fields. Using the handy Firebug extension I looked at the field--add-more-wrapper and didn't immediately see anything wrong. When I clicked the "Add another item" and the ahah callback fired, Firebug updated and showed me that there was a duplicate field--add-more-wrapper.

Worried that this was perhaps due to some other modules form_altering functions, I did a fresh Drupal 6.9 install and fresh CCK 2.1 install and enabled the text field. Then created a generic content type with only one additional field that was a multiple text field that allowed for unlimited values. This "all fresh" setup also exhibited the same problem. I am also using Firefox if that may affect this issue.

I am not sure if this is an issue where the #ahah['wrapper'] is pointing to the wrong element, or if something else is happening. Maybe someone else can verify this or shed some light on it.

Also, I have attached two screenshots that show the default 2 fields along with Firebug's view of them, and then an after shot that shows 3 fields and the erroneous duplicate ids.