Hi,
it seems there’s a problem with the default-originate parameter for a bgp peer:
- in Winbox, one cannot set “always” and its “if-installed” by default
- if set from terminal, and disabled/reenabled from Winbox the default-originate is set back to “if installed”
Please fix this, because it happens that one router might not have a default route installed in the routing table, but should advertise a default route for downstream routers.
The reason for the router not having a default gateway is because it receives a global bgp table so there’s no point in having a default route when you have routes for the whole internet 
Quick workaround is to have a default static route, however it may be a problem when using 2 or more upstream providers with global routing tables.