onSurface=true not working in summon mechanic

• summon{type=Chains_of_Void_Portal_3;amount=1;radius=0;yRadius=0;onSurface=true} @selflocation{ForwardOffset=-9}

for example, a mob spawned like this is spawning whenever the player is looking instead on a solid block. seems like onsurface is not working at all in this mechanic. please fix it thank you!