That is normal.
Massage out the cramps and do it again.
Cramping is to be expected when you take muscles into shorter range of motion because blood flow is cut off and the muscles become a bit hypoxic which leads to cramping. Since there's a lot of actin-myosin overlap, cramping is exponentially more likely when a muscle is short than when it is long.
Once your body gets used to it (usually over a couple of weeks) it will go away.