Disappearing Armor

I was playing on a server (No Bukkit) and i made some armor. After some time i logged off and when i came back on my armor was gone. So i made some new armor and i logged off again and logged in and my armor was still there. But after some time it disappeared again.

What I expected to happen was...:
When logging in that my armor would be there

What actually happened was...:
My armor disappeared...

Steps to Reproduce:
1. Get some armor on a server
2. Put it on
3. Log off (maybe close the server?)
4. Log in and look if your armor is still there