It's not a bug, but it's really dangerous.
Sometimes we must force user to select a mandatory value with dropdown list. And sometimes it's optional.

But with the mandatory dropdown list in bulk edit, the first value is selected by default. When you wish apply the same change about one field different of the mandatory one, you will be surprise that other field has changed. For example :

firstname;lastname;gender;payment
John;Deo;M;Unpaid
Scarlette;Johanson;F;Paid
Angelina;Joli;F;Paid

If you want to update John Doe line in Paid, Scarlette and Angelina will became "M".

The best solution is phpgrid add automatictly the first empty item for all dropdown list in bulk edit form. The bad solution is customed your dropdown list with empty item :

"edittype" => "select",
"editoptions" => array("value"=>':;M:Male;F:Female'),

This is a bad solution because the field may be NOT NULL and it will generate error on add/edit mode form.

Hope phpgrid can add automaticly the empty item in a dropdown list in the bulk edit mode.

Thanks