Forensics fixes/tweaks.

code/game/objects/effects/decals/Cleanable/humans.dm

@@ -34,6 +34,7 @@ var/global/list/image/splatter_cache=list()
 		invisibility = 100
 		amount = 0
 		processing_objects -= src
+	..(ignore=1)
 
 /obj/effect/decal/cleanable/blood/Destroy()
 	for(var/datum/disease/D in viruses)

code/game/objects/effects/decals/Cleanable/tracks.dm

@@ -121,7 +121,8 @@ var/global/list/image/fluidtrack_cache=list()
 				updated=1
 
 		dirs |= comingdir|realgoing
-		blood_DNA |= DNA.Copy()
+		if(islist(blood_DNA))
+			blood_DNA |= DNA.Copy()
 		if(updated)
 			update_icon()