Humanoid automatically sits when welded to another?

Whenever I try to weld a player to another it always forces them both to sit, anyone know why this happens?

game.ReplicatedStorage.remoteevents.Abilities.Carry.OnServerEvent:Connect(function(p,echar,carrying)
    local char = p.Character or p.CharacterAdded:Wait()
    if carrying == true then
        char.HumanoidRootPart.CFrame = CFrame.lookAt(char.HumanoidRootPart.Position,Vector3.new(echar.PrimaryPart.Position.X,char.HumanoidRootPart.Position.Y,echar.PrimaryPart.Position.Z))
        repairlimbs(echar)
        echar.HumanoidRootPart.CFrame = char.HumanoidRootPart.CFrame * CFrame.Angles(-90,0,0) + Vector3.new(0,3,2)

        local weld = Instance.new("Motor6D")
        weld.Parent = workspace
        weld.Part0 = char.Head
        weld.Part1 = echar.HumanoidRootPart
        weld.C0 = CFrame.new(3,1,3)
        echar.HumanoidRootPart:SetNetworkOwner(p)
    end
end)