Saddle should not rock when new.
Most far-Eastern lathes have American style inverted-V + flat bedways that tend to become a better fit with wear, unlike flat bed lathes that become loose as the shears wear.
Mini-lathes and the SC4 all have adjustable plates under the shears to stop the carriage rising, I'm sure you will find these on most Chinese (and other) lathes. But lathes are designed so that under normal cutting forces the carriage is pushed down onto the lathe bad and these plates do not do anything. They do function when parting with an inverted tool at the rear, for example.
Neil