There aren't networks statically created to be syncronized o not (in "/routing bgp network" there are no entries) but RB continue to annunce them.
This behavior happens when there are ring networks: when the main backhaul dies, the ring does not backup
Mikrotik replied that:
Advertisements of nonexistent routes sometimes may happen. It will be fixed in new
routing package.
The only method to resolve it is to manually find the RB that have the bad behaviour and restart it.
Chupaka it never happened in your network?