Bulk Settings : Negative Values Not Allowed For Relative Changes To Target CPA

1) Open a CPA account
2) Go to Bulk Settings page
3) select an element to modify
4) select 'set Target CPA' checkbox
5) select relative value in the dropdown menu
6) enter a value of -1
7) select the OK button at bottom of page

An error page is returned stating that a value of -1 is not acceptable.

This makes it impossible to lower a CPA value using this interface.