I've also experienced this barrel bug. The 1st time it happened to me, I left the barrel in the dungeon alone, teleported to the merchants area, verified that my items were all still there in the barrel, and they were. Now I just ignore this bug when it occurs. Hmmm...I never thought of adding items to the dungeon barrel to save trips to the merchants. That would be quite handy for when you don't have the teleporter stones yet or for when you lose them later.

"There's a great many people in this world, who through no fault of their own are sane." However, I am not one of them!.......Tomcat