Binding source Collection gets updated without updating it

I have a situation in which i have grid view which shows item name and the other grid view which shows item quantity a seprate grid view item quantity is like **DefItem**.**itemQuantity** Every thing is loaded through a context

Var qry=context.defItems. Include("itemQuantity") ;

Now when i try to make a new

foreach(ItemaQuantity itq in ItemQuantityBindingSource) {
objItemQuantity=new context. ItemQuantity () ;} ```

And load some data to it
Then want to load a nseted item 
```ObjItemQuantity.defItem=new defItem;"New Name";```

It throughs an error on foreach loop that collection is changed