I was getting a bit tired at this stage. That often messes big time with my riding ability. So when I came to a normal corner, stomped on the back brake and overshot it in a big way I figured it is time too slow down, pull myself toward myself and get going again. At the next corner I did the same but now I noticed that the rear brake feels "strange". And this was true, when I looked down I saw that the front part of it had fallen off and I was using the much less effective "air brake" version. This messed me up for a little bit until I adjusted my foot so I could still push on the remaining part of the lever to slow down. It took a while for the brain/foot adjustment to get the right pressure but after a while this sorted itself out and it worked just fine in most (note - definitely not all) attempts at cornering.