Had a similar problem last week. I was reading a thread about co2, looked over at my bike and noticed a flat. I patched the tube and did 2 rides for 75 miles with no problems. On Saturday, I was 4 miles into a century and the tire was soft. Pulled out the tube and couldn't find a leak so I pumped it up and finished the ride. The next morning it was flat. I just figured that Jesus loved me.