after discovering that USAir doesn't allow open jaw award travel(thanks usair board) trying to see if the return can be the start of my next RTW.

the star alliance calculator appears to allow me to do:

YYJ-yyz-EWR-sfo-NRT-PVG-SIN-LHR LGW-PHL-den-YVR

it says that there's impossible connection to leg 6, LGW-PHL. can someone pls explain why?

it appears to let me do the backtracking transcontinentally. is this a star alliance calculator screwup or real?