Do your hips round under during the dip in the jerk?

The correction is very simple. Watch the short video to see what we're talking about

Hip Stabilization
Use a wall or a pole and keep your hips sliding up and down the wall/pole. This will help you keep your hips stable to support the load on your shoulders.

Legs
Your legs are the only moving part of the body that is actually doing the upward and downward movement of the jerk. When you dip, keep hips sliding up and down the wall, make sure feet are making full contact on the floor not just the heels. This is important because if you distribute the load on the heels unfortunately this can cause the hips to roll under. Full foot contact on the floor. Then, just move up and down and practice the movement.