Proof of missing and vanishing items!
 

These pictures show how my items go missing...

I cant see nothing o.o

look again ...

WHO WILL IT HAPPEN TO NEXT!!!!

It never happened to me, so I can't help you ^^

you cant help me anyways..... no one can <struggles in his straight jacket>

Demon, you aren't fooling around with certain files now are you. ;) You did say you were a programmer, so you probably know what I am talking about.

yep i made a bow that does damage 9999-9999 damage... no no...

I think the error is in some kind of weight calculation the number is not available from your character screen but if you keep on getting loaded with stuff you'll get to a point where your character has reached its weight limit and will run slower than if he's just overloaded.
Some of the items won't show up and you have to give some items to another player, or sell your loot then relog to view the rest.

now if this secret number where a player has reached it's capacity limit is in the calculation when viewing items he won't be able to see a certain amount of items.

Blunt examples:

someone has a weight limit of 20 and a capacity limit of 40
plate armor 5 kg
shield 5 kg
bow 5 kg
staff 4 kg
hammer 6kg (at this point 25 kg, weight limit reached) #1
tunic 3kg
gloves 2kg (-.-')
helm 5 kg
sword 5 kg (at this point 40 kg, capacity limit reached) #2
spear 6kg
mage hat 2kg

Let's say these items were looted in the direction they are listed, at some point (I don't know if it's random or something) the user won't be able to view the spear and the mage hat (possibly not the sword either) because they exceed his capacity limit.
If it's in the order these items were created that they disappear from your list I don't know, this is just a theory I have, but it would seem to be the most logical, actually I think it was the oldest items which disappeared from mine last time it happened to me

Demon monger: Do you know assembly language? You can answer in pm if you want

Happened to me yesterday, I had pierce arrows selected and then switched to slashing arrows, but when I tried to reselect the piercing ones they had just vanished. And no, they haven't finished! And yes, I'm pretty sure that it happened the way I describe and I can add that although I lost my arrows in the inventory I still had the icon on my short bar.

And I don't know about the weight limit theory AwD, I don't train for some days so my weight I pretty stable and still it happened yesterday.