If you keep moving the mouse up, you reach the max upward aim restriction, and then quickly aim down as far as you can, you can get past the downward restriction. You can also get past the upward restriction by doing those steps vice versa.
Once you move your mouse back in the "restricted" range, the restrictions are re-applied, so it's not a huge deal but should still be fixed.
If you keep moving the mouse up, you reach the max upward aim restriction, and then quickly aim down as far as you can, you can get past the downward restriction. You can also get past the upward restriction by doing those steps vice versa.
Once you move your mouse back in the "restricted" range, the restrictions are re-applied, so it's not a huge deal but should still be fixed.