pfSense

How to recreate:
Create L2TP VPN
Create a default gw to the VPN subnet
Create the static route

• route is added to diagnostics -> routes
  Disconnect from VPN
• route is deleted from diagnostics -> routes
  Reconnect to VPN
• route is not re-added
  Disable the static route
  Enable the static route
• route is added to diagnostics -> routes

The static route should be automatically re-added when the L2TP interface is up.
I'm not sure if this is an intended behaviour, I googled it, and I didn't found anything related to this - so I assume that this is a bug.