Is your OpenVPN a "Server" or "Client" configuration? Do you want both "Inbound" and "Outbound" auto-rules to be created?
I have a fix that will add "Outbound" auto-rules for a OpenVPN "Server" config, and add both "In/Outbound" auto-rules for a "Client" configuration….
Typically, with OpenVPN, you assign an interface in the Interface tab, and it will show in the pfBlockerNG In/Outbound Interface options. The checkbox option, is for some corner-cases where there is no interface assigned and there is no Interface listed in the drop-down menu.
My OpenVPN is a server configuration (think "road warrior" setup with mobile clients connecting). So my use case is that I want to apply the same PFBlockerNG outbound rules I use for local clients to road warrior clients connected through the VPN for ad-blocking and content blocking purposes. So it sounds like your fix would address my problem.