Hello,
i have table with primary key column defined as char(4).
The table contains only single row with key value "A" which is physically stored as "A " because it is char(4).
In the code I have (note the id value with and without trailing spaces):

MyTable o1 = (MyTable) session.get(MyTable.class, "A ");
MyTable o2 = (MyTable) session.get(MyTable.class, "A");
MyTable o3 = (MyTable) session.createCriteria(MyTable.class).add(Restrictions.idEq("A ")).setMaxResults(1).uniqueResult();
MyTable o4 = (MyTable) session.createCriteria(MyTable.class).add(Restrictions.idEq("A")).setMaxResults(1).uniqueResult();
System.out.println(o1 == o2);//prints false
System.out.println(o1 == o3);//prints true
System.out.println(o1 == o4);//prints true
System.out.println(o1.getMyKey() + "|" + o2.getMyKey() + "|");//prints A |A|

All instances are surely associated with the same database row (there is only one row in the whole table).
Instances o1, o3 and o4 are the same Java instances (==), instance o2 is different.
Criteria behave consistently - db identity leads to Java identity within session.
Session.get() behaves inconsistently - Java identity is broken within session.

In Hibernate reference i read "Within a Session the application can safely use == to compare objects.".
In the case of session.get() it seems to me that this might not be always true.