When the Browning fires the extractor claw is hooked over the case rim and pulls it rearward out of the chamber and toward the ejector. When the ejector impacts the rear of the case it is rotated out from under the extractor claw and out the ejection port.
Fired cases being extracted from the chamber ride higher than the last one. This is because they ride over the top of the cartridge waiting to be chambered and cannot slide lower down, as can the last shot in the pistol.
On all shots except the last one, the fired hull cannot go lower than the top of the next cartridge in the magazine. On the last shot, it can. If the case is not held against the breechface by the extractor, it can slide downward more than when another round’s in the magazine. The magazine follower does not ride higher than the magazine lips; a cartridge in the magazine is partially exposed and higher. This allows the ejector to strike the rear of the case higher than for the subsequent shots and can result in the case not being fully ejected. Normally, it causes no problems at all and the case can either be shaken out of the Hi Power or will follow the magazine when it is removed from the gun. If you happen to drop the slide and the fired case attempts to chamber backwards, it can cause a slow-to-clear jam.
Here you can see the breechface and extractor claw on the Browning Hi Power. If the case is not held quite firmly enough, the last case can slide lower and not be kicked out of the pistol.
Look at the position of the ammunition in the Hi Power magazine. It is higher than the magazine follower is when the magazine is empty. This contributes to the last hull sometimes failing to completely eject.
I have a Hi Power that fails to eject the last round and it’s caused me zero problems. If you wish to avoid it completely, the cure is usually some light filing away of metal on the inside of the extractor arm ( at the pad) to allow the claw to move a tiny bit more inward. Where this point is becomes obvious after removing and examining the extractor. This allows the extractor to hold the fired case more securely against the breech face. Usually this solves the problem. Before doing that, I strongly suggest making sure that the channel in which the extractor rides is clean. Crud can build up in there to the point that the extractor cannot ride inward enough to fully do its job. Sometimes a new extractor spring is required as well. A very few strokes of the file and then smoothing are all that’s required, but if you’re not sure what to do, pay for the services of a gunsmith. The fee should be nominal, but replacing a ruined extractor would not only be more expensive, but embarrassing.
Best.