4.7 forms api checkboxes results array in hook_submit adds extra value when checkbox list is empty.

This is driving me mad. I have a form that returns search results that also re-draws the same form for additional searching right after the results. I'm using the forms API "checkboxs" type. The user can select some or none of the checkboxes. I'm using 4.7.5

• When my forms api "checkboxs" list have selections made already, and the user de-selects them all, everything is ok.
• But when that page is again submitted where the checkboxes were empty to start with when the page was first drawn, I get an extra 1 in the result array!

This is my hook_submit:

function project_finder_form_submit($form_id, $form_values) {

  //dprint_r is from the devel module for debugging
  dprint_r($form_values);

  $locationList = '';

  if (is_array( $form_values['phaselist']  )) {
    $phaseList = convert_array_to_comma_delimited_string($form_values['phaselist']);
  }

  .
  .

I do not tamper with the result set. And look at what I get back from the devel debug function: What the heck are those extra array entries in my submit result???

Array
(
    [keywords] => 
    [phaselist] => Array
        (
            [] => 1
            [1] => 0
            [2] => 0
            [3] => 0
            [4] => 0
        )

    [countries] => Array
        (
            [] => 1
            [17] => 0
            [18] => 0
            [19] => 0
            [23] => 0
            [60] => 0
            [20] => 0
            [21] => 0
            [22] => 0
            [16] => 0
        )

This is doing a lot of harm to my code - can anyone reproduce this?