I have created a Popup window and set it as Floating
It does not want to open at the floating coordinates, cant figure out what I am doing wrong?
I assume you’ve got open centre turned off?
I didn’t actually know you could use these coords to set the window open position 
I would normally set the open position from script. I’ll have to get back with an example, as it seems with all my work in Perspective, I’m a bit rusty!
This would be my first check.
Another thing you can try to set the Popup windows' Cache Policy to Never and test again. (This will ensure the popup always opens at the specified location because If the popup is movable then it open where the user last opened it.)