animatedIcon vs icon, activeIcon

[mlleo]

I just tried to implement simple expandable floating action button case with this package, and used icon, activeIcon property for main button Icon. But when I moved to other page by clicking the child button, and then when I came back to main button, the icon of the "icon" property moved (the location is changed, at first it was at the center of the main button, but now it moved to partially outside of the button).

But when i used animatedIcon property, it does not occured, but there is no exact customized pair (+,x) so I cannot use that property.

Does anyone know why the animatedIcon, and icon+activeIcon property works different?