The reactive sputtering process involving two reactive gases has been investigated. Sputtering titanium in the presence of oxygen and nitrogen in argon was studied by means of optical emission and mass spectrometries. The experiments reveal the mechanism of the mixed target poisoning. Increasing the nitrogen supply in the presence of a constant oxygen supply forces the reactive sputtering system to avalanche from a high-rate metal-sputtering mode to a low-rate compound-sputtering mode at a lower N-2-to-Ar ratio as compared with the single reactive gas Ar/N-2 reactive sputtering process. The amount of the oxygen admixture, however, also affects the character of the avalanche and the corresponding hysteresis effect. At a definite level of constant oxygen supply the Ar/N-2 processing behaviour becomes irreversible, successive decreasing of the nitrogen supply to zero in this case is not sufficient to force the process to return back to the high-rate metal-sputtering mode. A "process trapping" effect appears. The coupling effect between the consumption of both reactive gases N-2 and O-2 during increase and successive decrease of N-2 in the presence of a constant O-2 Supply is reflected in the dependencies of the respective partial pressures. The cause of the observed trapping effect, the shift and the change of the character of the sputtering rate hysteresis curve may be explained in terms of the link between the consumption of the reactive gases and the corresponding target condition. The experimental findings support the theoretical model of the two-gases reactive-sputering process recently presented by the authors.