To reproduce:

1. add a MenuButton
2. add a CustomMenuItem to the MenuButton
3. remove the default content node of CustomMenuItem, the CheckBox
4. add a Circle to the CustomMenuItem as the content node. Or add other component that doesn't have the graphic property.
5. drap another Circle hover on the first Circle.

Bug: the graphic placeholder appears, and when releasing mouse, the graphic placeholder is still there, also it can't be removed by selecting it and press "Delete" key.

This doesn't happen outside CustomMenuItem.