How to get "Found shared references to a collection"

Fix_Found_shared_references_to_a_collection.cs

var coll = new UIRColl();

var u1 = new user();
//u1.uircolllection = coll;
u1.uircolllection = new UIRColl(); 
u1.uircolllection .AddRange(coll);

var u2 = new user();
//u2.uircolllection = coll;
u2.uircolllection = new UIRColl(); 
u2.uircolllection .AddRange(coll);

session.flush();

Found_shared_references_to_a_collection.cs

var coll = new UIRColl();

var u1 = new user();
u1.uircolllection = coll;

var u2 = new user();
u2.uircolllection = coll;

session.flush();