This article investigates the OBI phenomenon in RFoG systems. Laser behavior leading to OBI events is theoretically described and laboratory experiments to investigate its effect are performed. The results show that RFoG OBI can occur prevailingly and involve more than 90% of the RFoG ONU population. Results also reveal that the preamble of DOCSIS signals is robust to the RFoG OBI problem. The concept of OBI pairs and groups is introduced to offer error-free operation. Finally, potential solutions to the OBI problem are described, which clearly demonstrate that any single-wavelength OBI-free solution for thermally-uncontrolled RFoG system must involve the CMTS support.