Everything sounds completely normal Michael. Flaps add lift and drag (simple terms here, you have seen the response of the model), so are used to improve takeoff at small flap angles, and to steepen the approach without increasing the models approach speed (drag control). The hint is that the flaps are used at the low end of the models speed envelope. Actuating the flaps at higher speed results in the response you have seen. The next time you are in the circuit try lowering them in steps, if the model starts to climb, reduce the throttle. When the thing stabilises, lower a bit more flap, watch the response, lower the throttle again. You will soon see what the model needs, add down trim if you need, but do all this at low airspeeds. Do not use aileron in large amounts, at lower speeds that could result in untidyness, use the rudder, control speed with elevator, height with throttle, all classic stuff. Flaps are useful, but only when you have a need for them. If you have a short strip, with high obstacles around, then they can be necessary on some models, otherwise they look good, but ain't needed.
Evan, WB #12.