Disappearing dynamite SP?

[Judge Lazar]

Trying to bomb this damn train in a tunnel, I set my TNT down by an easily identifiable object and it seems like it's disappearing after a couple minutes. I'll be looking right at it with the red crosshair on the scope, drop the scope for a second, bring it back up and the TNT is gone. Can't tell if I'm just not seeing it because it's pitch black and the stick blends into the ground texture or what.