OpenVPN - tap interfaces and default gateway

All appears to be fine except that a default gateway just isn't 
set when checking 
...
push "redirect-gateway def1"

If you use that option, then you don't set a default gateway. Instead two routes should be added for 0.0.0.0/1, and 128.0.0.0/1 to your VPN.

I realize this is an old question, but I wanted to add that in my experience, if everything works EXCEPT for the setting of a default gateway, running OpenVPN as administrator will solve the problem on Windows 10.