Something like that happened to me. Early summer when I finally pulled my bike out for the first time this year, I took her for a blast down the road and the first time that I hit the brake, the pedal seemed like it went down a little further than usual. One of the next times I took her out for a quick ride down the road before starting to clean my garage, I parked it outside and cleaned my garage. Hours later I jumped on my bike to put her away, rode around my garage and hit the back brakes and I had zero back brakes! After pumping the rear brake pedal they did come back but still didn't feel right. It feels like there is almost a little resistance at some point (almost like a metal to metal feeling) when applying the brakes. Well it was still under warranty till the end of August so I took it to the dealership and told them what happened and I was thinking that the master cylinder was bad. They called me a couple days later and said that it was done. They said that it had air in the system and is a little common because the caliper is located higher than the master cylinder. He said the same thing happens on Honda Goldwing's when they sit for extended periods of time without riding and depressing the brake pedal from time to time. I am not buying it, air would have to be getting in the system somehow. My brakes are still not 100%. It still feels like there is a little resistance at times, which still leads me to believe that the master cylinder is bad. Any thoughts ???