Missing some data stored through object caching in memory

Question

I'm using ASP.NET MVC3.I've cached some data using object caching in memory.In some cases,it opted out some caching data. for example.
I've stored array of integer number;

int[] i;

i[0]=0;

i[1]=1;

i[2]=2;

i[3]=3;

i[4]=4;

i[5]=5;

and cached array i;
In some cases, when i retrieve array,it will display only 3 elements.it will opted out first 2 elements and after that i never get those first 2 elements until i restart application from IIS or remove it from caching using remove method.
I cant figure it out what is wrong. What could be the reason?