Removed widget remains on parent - kivy

Question

I have parent window that is Widget where places another widgets (parent.add_widget(...)) by right mouse click. Also children widget can be removed by middle click (parent.remove_widget(...)). And here I faced strange issue - child actually removed from children collection of parent but remains visible (but inactive. i.e. all interactions with removed widget image are impossible). I do not using any layouts because children are movable to any point and thus should not be aligned somehow.
Question: how to redraw parent after remove_widget?
Example code:
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.config import Config
from kivy.lang import Builder
from kivy.uix.behaviors import DragBehavior
from kivy.uix.relativelayout import RelativeLayout
Config.set('input', 'mouse', 'mouse,disable_multitouch')
Builder.load_string(f'''
<Node#RelativeLayout>:
drag_rectangle: self.x, self.y, self.width, self.height
drag_timeout: 10000000
drag_distance: 10
canvas.before:
Color:
rgba: self.bcolor
RoundedRectangle:
pos: 0, 0
size: self.size
radius: [10,]
''')
class Node(DragBehavior, RelativeLayout):
def __init__(self, **kwargs):
self.bcolor = (0, 0, 1, 1)
super(Node, self).__init__(size=(100, 100), **kwargs)
def placement_pos(self, x, y):
return (x - self.node_width() / 2, y - self.node_height() / 2)
Builder.load_string(f'''
<GrapherUI#Widget>:
canvas.before:
Color:
rgba: {.5, 1, .5, 1}
Rectangle:
pos: self.pos
size: self.size
''')
class GrapherUI(Widget):
def __init__(self, graph=None, **kwargs):
super(GrapherUI, self).__init__(**kwargs)
def on_touch_down(self, touch):
touched_children = [x for x in self.walk(restrict=True) if x is not self and x.collide_point(*touch.pos)]
has_touched_children = any(touched_children)
if touch.button == 'right':
if not has_touched_children:
self.add_node(touch)
elif touch.button == 'middle':
self.remove_node(touched_children, touch)
super(GrapherUI, self).on_touch_down(touch)
def add_node(self, touch):
print('add node')
with self.canvas:
node = Node(pos=(touch.x, touch.y))
self.add_widget(node)
def remove_node(self, touched_children, touch):
for node in touched_children:
print('remove node')
self.remove_widget(node)
class Main(App):
def build(self):
return GrapherUI()
if __name__ == '__main__':
Main().run()

Answer 1

Well, as usual with Kivy nobody except yourself could help (even documentation). Here issue caused by with self.canvas: line under add_node method. If it removed widget disappears after removing.