As someone that owns 5 Mosins Variants, I have never seen or heard of this feature before and just assumed it was a bug of some kind in game. If some has a source that would be great.
You are correct. All, without exception WW2 Nagants and K98's work the same way. Standard bolt action. Fire, pull bolt to eject shell and push bolt forward to load next round.
If you pull the bolt back again to load an additional round you will eject the one in chamber. There is no interrupter, or anything else in any of them. It doesn't exist and for those saying it does, you have to start shooting some firearms and getting to know something about the actual real life versions of the guns.
(Have I mentioned in other threads that I hate when people post stuff about the guns when they don't actually know anything about the real thing, don't own any guns and have not had any actual real life experience shooting them? If not, I say it now, I hate that because this thread is driven only by lack of knowledge of the real thing.)
I've owned and been shooting both rifles for over 20 years, have seen thousands of examples of each and without exception they all work the same. No mystery here. It is a bug in game, there is no special mechanism in the real world.