Pokemon Go question, I'll keep this short. I had a slowbro with a mouse's hair of cp bar left. I hit power up just to get that last smidge in, but instead the bar itself grew longer! What does this mean? What is going on with max cp?

I'm now trying to top out a beedrill to see how much longer his bar will get, does this mean that with a major and senseless investment of stardust, even a Beedrill can be slowly pushed up to 1400+?