Can't get to show RPG Interface demo/popup_demo.xml on center of the screen

Hi Lars and great people from Level Up Labs,

I have a popup based on RPG Interface demo/popup_demo.xml to show up at center of the screen
I got a map and If I set camera movement using
FlxG.camera.follow
popup seems to be stuck at x=0, y=0 and there it is visible
I can't get to work popup based on RPG Interface demo/popup_demo.xml (https://github.com/HaxeFlixel/flixel-demos/blob/dev/User%20Interface/RPG%20Interface/assets/xml/popup_demo.xml)

If I set

FlxG.camera.x = 100;
FlxG.camera.y = 100;

I expect it too be in the center of screen

I looked the code of class Popup_Demo extends FlxUIPopup and it seems that it should set scrollfactor to 0

Start with the referenced User Interface/RPG Interface/assets/xml/popup_demo.xml and the Popup_Demo class extending FlxUIPopup. Reproduce the popup while using FlxG.camera.follow or changing FlxG.camera.x and y, then inspect how its position and scroll factor are handled. Done means the popup appears centered on the screen while the camera moves.