I had found 4 throwing spears. I am in Novac now so I saw a dumpster so I put some stuff there. Well I put my 4 throwing spars inside, and all of a sudden I have 6 throwing spears? I thought ok, I missed it, so I put them inside as well. Well they never showed up? So I was puzzled, reloaded and same thing again. First it shows up as 4 throwing spears then when I put them in the dumpster, I have 6. Well this time I will keep them.

So is this normal or just another glitch on the 360? Is there anything else I should be aware of?

This is the duplicate item glitch.

It can happen to seemingly...ANY item. Although its far more common with armor and weapons that have a 'condition' stat.

Instead of doing simple arithmetic (which any of us can do in our sleep) the game adds the two inventory items together but they sort of occupy the same 'spot' in your inventory.

For weapons with variable condition (like the 10mm pistols this happened with for me) you will have 3 + 3 pounds of equipment but only have access to one of the guns. This, of course, means you can't repair one with the other.

This is the first I've heard of this glitch happening in random containers in the world. It happened in my personal inventory and in my personal wardrobe in the Novac safehouse.

You just have to sell/drop one group of them and only pick up one set of the throwing spears. Or sell both groups. Or use the 4 on enemies and the 6 will magically reappear in your inventory.

i had this happen with a boomer outfit.. got one from a reward and then found a dead one and looted it and i picked it up but it is hidden under my other outfit in my inventory.

Throwing spears seem to be the most glitched of the replicated items.. It showed seven in my inventory but I actually had 42.. They at least sold as 42 separate spears. I decided not to pick up anymore spears.
The only other item I"ve had this happen to so far is the BB gun.. Had two but only showed one in my inventory. Again I could still sell one and keep the other.

This happened with my spears as well - the count in my inventory is some insane number bearing no relation to the correct number - which always shows up on the HUD.

Doesn't seem to be a big deal, relatively speaking.