OpenVPN and default route

[sephora]

Hi everyone!

I've got a (hopefully) simple problem with my VPN.

My VPN server is running on my Gentoo router. I posted my setup here: https://forums.gentoo.org/viewtopic-t-1166185-start-0-postdays-0-postorder-asc-highlight-.html

I recently added a bridged wireless AP to my VPN. A BPI-R3 with LTE modem to be specific. It currently runes OpenWrt. Which works fine at the moment.
Setup is as follows:

• I dial-up the modem and start the VPN client on the BPI.
  
• That brings up a tap device which is bridged into the Lan on that router.
  
• The Lan bridge on the BPI has a static IP.
  
• DHCP is handled by Dnsmasq running on my Gentoo router.
  

Now the problem:
Every clients that connects while the VPN tunnel is active gets a IP but it doesn't get a default route.
This problem is only present if I connect via VPN. In any other case I get the correct default route.
If I manually add a default route everything is fine. And I can confirm that my VPN-tunnel works.

Unfortunately I have no clue why I don't get a route.
I played a little with the VPN config, i.e. switching 'push "route-gateway dhcp" ' on and off. But that doesn't seem to do anything.
And since the network is bridged it should be easy to get the route from Dnsmasq, like every other client in my Lan. Right?
So... What am I missing here? Does someone has any idea?