drag behavior with initial position in float layout

drag.py

from kivy.app import App
from kivy.lang import Builder
from kivy.factory import Factory


KV = '''
<Floaty@DragBehavior+Image>:
    size_hint: None, None
    size: self.texture_size
    drag_rectangle: self.pos + self.size
    canvas:
        Line:
            rectangle: self.pos + self.size

    on_touch_move:
        touch = args[1]
        uid = self._get_uid()
        print(self._drag_touch is touch and touch.ud.get(uid)['mode'])
        if self._drag_touch is touch and touch.ud.get(uid)['mode'] == 'drag': self.pos_hint = {}

FloatLayout:
    Floaty:
        source: 'data/logo/kivy-icon-128.png'
        pos_hint: {'center': (.5, .5)}
'''

class Application(App):
    def build(self):
        return Builder.load_string(KV)


if __name__ == "__main__":
    Application().run()