Can you tell me how paralysis or loss of motor control of the legs can occur without a loss of sensation?

Difficult question: It is possible to have a lesion (ie. Tumor or stroke) that affects the motor regions in the brain but spares the sensory cortex. Don't forget that there is a topographical MAP in the brain where specific functions are localized. For example, a tumor in the midline can press against the areas that control movement of both legs at the same time sparing the sensation.