Deleting a form field in Adobe Acrobat XI

I seem to have encountered a bug in Adobe Acrobat XI.  I have a pdf document with form fields, and I am completely unable to delete a certain field (which I didn't intentionally create). The field is invisible and displays no name, and the "Highlight Existing Fields" option does NOT shade the field pale purple -- it's as if the field isn't really there.  Here's how it behaves (for ease of discussion I'll refer to the field as the "blank field"):

• In Form Editing mode, I can see the black outline of the blank field (with a tab order of 0). It has no name. I can point to the blank field and select it, and the outline turns bright blue with handles. When I press the delete key or right-click on the field and click "Delete," nothing happens. When I close Form Editing, the blank field disappears.
• If I view the Content pane and look at the individual annotations, I find two fields identically named (there is only supposed to be one field in my document with that name). When the first one is selected, the corresponding field outlines in faded blue; when I click the second one, the blank field I can't delete becomes outlined in faded blue (but still with no name). Pressing the delete key at that point doesn't do anything.

Whether or not the form field is tagged, I cannot delete it.  I also cannot modify its Properties to make it hidden.  I could start from scratch, but I've spent a lot of time on this form making it accessible, and I don't want to re-do it.  I need to get rid of this blank field!  How?  (P.S. This has happened to me before, so it's not just a fluke.)