Yes my bad, this is a debugging remnant because all UWP windows share the same name meaning that it gets very confusing when the settings and other applications get captured by WinWM, or like the wifi popup, etc...
Calculator is one of those applications that I set to floating in i3/awesome, so I'm not sure it should be "fixed". This is the sort of thing that users should be able to decide on the fly.
I'll address the bug soon