this is an very old bug. I used to have those all the time.
Also another bug on all mortars. The smoke bug, sometimes when you use smoke barrage at maximum range the crew just "freeze" in place and do nothing until you press Halt and use barrage again, very annoying bug when you are trying to coordinate a big flank and the smoke fails.
Seeing how much trouble mortars are bringing into the game I would say to just remove all mortars/Isgs and give infantry a smoke launcher like the usf one
About the smoke barrage; yeah its sucks.
But its the same to Ranger nades, sometimes thy threw it, sometimes not on max range.
Its coh2 We should allready adapt to this bugs