Most of times when i light a flare and i throw it, it dissapear, in fact, many times i can find this flare again where i found it at first.
In this case i found the flare in a restaurant on Sveltojarsk's place, light it and throw it in Svetlojarsk's church.
Light a flare move(maybe move in another building) and throw it.
Test it again, i find one in a vegetable store, throw it in a train station, work fine, then throw it in a empty wagon, flare get back in the Train station. So not the exact same place i found it at first.
I take it again throw it on the road, it dissapear.
I get back to the train station and nothing, i get back near the empty wagon and i think i saw it before the light turn off.
So i get back on the road where i trhow it and here it is.
whenever you light a flare regardless where you stand the flare will disapear after trowing