I have a set of objects present in an object(X). I copied these set of objects into new object(Y) and trying to save the new object(Y). After saving when i see the size of the set in the new object(Y), i am finding the size less than the one which i inserted into new object. Before save its displaying the correct size, but after save it shows less.
Is this problem with Hibernate save?

Well, this isn't a problem with Hibernate. Basic saves are implemented properly.

Show us some code. Just a snippet, and maybe we can have some suggestions.

Do you commit your transaction as soon as you have copied the list. Maybe some funny business happens before the commit happens?