It very well can be that the servos are drawing enough current from the RX pack that it drops the voltage enough for the SR300 to brown out. I had that happen to me and the "glitch" buster capacitor saved my day. A lot of high speed and high torque digital servos can be very power hungry and your receiver may be a bit more power hungry than the specs state.

Spektrum glitch buster is about $5.00. It's a 16V 4700uf cap.