Today, after warmup, we worked a little more in lengthened canter. I asked him to lengthen down the long side and shorten on the short sides. The first time I asked him to go, I got nearly no response. The second time, he went forward and lengthened a bit. The third time, he did a very hesitant buck as if he was afraid of being chastised for lengthening his canter. I still sent him forward and he went. He also came back very nicely.
After that we did some jumping. He grows more confident all the time.