This is not "normal"...but unfortunately fairly common especially for the more temperamental cultivars. The cause is draught stress almost undoubtably. This is the natural reaction to a lack of water getting to the leaves for cooling during the summer heat. It may not be due to lack of watering but more so due to too much sun/heat. Move them into part shade and water daily being sure to throroughly drench the rootball (unless they are planted out in which case you need to just water like crazy). It is always difficult to keep one year grafts alive especially during the heat of summer. I would recommend never buying them during these brutal months as the transport shock can kill them when they are that small. Your trees might make it or they might not; I have experienced both with those small grafts.