I THINK that I may be able to answer two of your original concerns.
Have you ever ejected a still partially loaded mag and found the top round sticking further forward(out) from the rest? The reciprocation of the slide causes the round being chambered to drag the next one in line a little bit forward also. This obviously places it closer to the feed ramp for its "turn" to chamber.
Now, when you loaded the round alone, you no doubt pushed it in under the feed lips, and all the way to the rear? Since the action above had not occurred, the round was able to nose dive when the breechface impacted the rim. It pivoted, if you will, under the lesser spring tension against the follower with only one round in postion. This would not tend to occur with a loaded mag, because there would be no room to allow it, and the spring is exerting greater tension.
Pulling on the trigger to any extent probably causes at least some movement of the sear. I believe these have sear blocking safeties, ala the 1911? So, due to close tolerance fit, the sear itself effectively blocks the safety from being pushed up. When you cock the hammer, it resets properly, allowing the safety to function as designed.
Locking the slide to the rear with the safety is also done on the Hi-Power for field stripping. I do not know if this is the same operation that you described happening toward the end of your post. If anyone sees a flaw in my reasoning, please jump in to enlighten me.
It is not clear, but did you keep the .40 also, or return it? VL
