It maybe because of my medications but I can’t think of any case where if you have one reservoir going to two master cylinders how any fluid would be sucked out of the master cylinder in the intact system. There would need to be a T somewhere in the hose connecting the reservoir to the master cylinders and the T would act as a vacuum brake and the good system should be intact to stop the car. However using only one reservoir would require more frequent filling due to brake pad ware.

Bill Lomenick