Syswan router VPN passthrough has reverse setting

I've become a fan of Syswan routers as they are a cheap, functional business class router. There aren't a lot of routers in the sub $300 category that aren't the residential wireless routers that are sub $100.

Today, I was troubleshooting the fact that users at a site with a Syswan router couldn't make outgoing VPN connections. After checking, PPTP passthrough was enabled, so I disabled it. And voila - it worked. So it seems, in some cases (not all) - the PPTP passthrough box has the reverse of the intended effect. Screen shot below of a setting that DOES work for PPTP passthrough. The model of this router is Syswan Duolinks 24 VPN.