When the cck fields are in vertical tabs (http://drupal.org/project/vertical_tabs - now part of drupal 7 core) the bottons attach to more fields than just the node reference fields.
For example, I have the fields with the explorer like this:

When I look at other fields under different tabs the buttons are also attached like:

Comments
Comment #1
gnindl commentedThat's strange. Since version 1.1-beta3 Nodereference Explorer supports the Link field type. Therefore you have to attach an 'Explorer' widget. It seems like you have unintentionally done this here.
Comment #2
gnindl commentedMaybe an akward JS error. Link field types can have an explorer widget (apart from nodereferences). Nevertheless this error shouldn't occur any more with the latest development snapshot.