This is not unusual at all.
As you increase tension work on radial true, making the wheel round. It is possible to have perfect tension and still be out of round. On 8, 9, and 10-speed rear wheels the non drive side spokes will need to have about 60 percent as much tension as the drive side to center the rim (dish).
Do the final tension and truing with the tire fully inflated. This makes a significant difference.