Needs to duplicate the tree, because query plan compilation alters it.

Author: fredericDelaporte

src/NHibernate/Linq/NhLinqExpression.cs

@@ -73,7 +73,7 @@ public IASTNode Translate(ISessionFactoryImplementor sessionFactory, bool filter
 				// Query has already been translated. Arguments do not really matter, because queries are anyway tied
 				// to a single session factory and cannot switch from being a filter query (query on a mapped collection)
 				// or not.
-				return ExpressionToHqlTranslationResults.Statement.AstNode;
+				return DuplicateTree(ExpressionToHqlTranslationResults.Statement.AstNode);
 			}
 
 			var requiredHqlParameters = new List<NamedParameterDescriptor>();
@@ -96,7 +96,8 @@ public IASTNode Translate(ISessionFactoryImplementor sessionFactory, bool filter
 					.Except(requiredHqlParameters.Select(p => p.Name))
 					.Any();
 
-			return ExpressionToHqlTranslationResults.Statement.AstNode;
+			// The ast node may be altered by caller, duplicate it for preserving the original one.
+			return DuplicateTree(ExpressionToHqlTranslationResults.Statement.AstNode);
 		}
 
 		internal void CopyExpressionTranslation(NhLinqExpression other)
@@ -106,5 +107,15 @@ internal void CopyExpressionTranslation(NhLinqExpression other)
 			// Type could have been overridden by translation.
 			Type = other.Type;
 		}
+
+		private static IASTNode DuplicateTree(IASTNode ast)
+		{
+			var thisNode = ast.DupNode();
+			foreach (var child in ast)
+			{
+				thisNode.AddChild(DuplicateTree(child));
+			}
+			return thisNode;
+		}
 	}
 }