unable to edit custom data in tab if inline set already exists

to reproduce:

• create a custom data set attached to contacts and display inline (if one already exists you can skip this step)
• create a custom data set attached to contacts and display in a tab
• navigate to a contact and try to edit the set in a tab

result: the popup opens with the inline set instead of the tab set. it's not a popup-specific issue – if popups are disabled it still opens to the wrong data set.

this is a regression introduced in 4.7. I setup an example on the sandbox site:
http://dmaster.demo.civicrm.org/civicrm/contact/view?reset=1&cid=34

click the custom data set tab and try to edit.