The booster has the wrong moment of inertia when detached from the upper stage.

This rocket has an automated reusable booster. The upper stage detaches the booster and then switches to it. The booster will then flip around and boost back. After boosting back, the booster switches back to the upper stage. The upper stage performs circularization until the booster hits 30,000 m in altitude, then it switches back to the booster, which performs the landing.

However, when I don't allow the booster to switch back to the upper stage and follow it until it lands, the landing glide goes horribly wrong and the rocket is unable to land accurately or at all. It appears that the rocket maneuvers much more slowly than it should as if it has a larger moment of inertia than it should.

To reproduce the issue, disable AG 4 DURING the boost back burn. This should stop the booster from switching to the upper stage, therefore preventing the booster to be reloaded when the upper stage switches back to it (which updates its moment of inertia).