I'm not very familiar with Russian mortar rounds, but it appears that some of those rounds have their fuses in them. There are safeties in the fuses that require a set amount of time after firing before they arm, but storing ammo with the fuses in is a very big no-no. One malfunctioning fuse, and it can all go up.
Maybe they're storage caps, designed to keep the fuse well clean, but if that's the case, why don't all of the rounds have them? Weird.
I'm also a little taken aback that they are not boxed. Maybe that store is right next to a firing position and the rounds are prepped for rapid use. Still doesn't seem like safe storage to me.
Disclaimer: while I was a 60mm mortarman, I never saw combat, so I don't know if this storage matches what our forces do in combat. I just know that it gives me the boo boo jeebies to think about working around that kind of storage.