diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/mapping/identifier/composite/CompositEntityUpdateTest.java b/hibernate-core/src/test/java/org/hibernate/orm/test/mapping/identifier/composite/CompositEntityUpdateTest.java
new file mode 100644
index 000000000000..3ce08263c427
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/mapping/identifier/composite/CompositEntityUpdateTest.java
@@ -0,0 +1,212 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.mapping.identifier.composite;
+
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Embeddable;
+import jakarta.persistence.Embedded;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+import org.hibernate.cfg.AvailableSettings;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.Jira;
+import org.hibernate.testing.orm.junit.ServiceRegistry;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.hibernate.testing.orm.junit.Setting;
+import org.junit.jupiter.api.Test;
+
+import java.io.Serial;
+import java.io.Serializable;
+import java.time.Instant;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+@DomainModel(
+		annotatedClasses = {
+				CompositEntityUpdateTest.TimeScalePkOidDatum.class,
+				CompositEntityUpdateTest.TimeScalePkOidDatumEmbed.class,
+				CompositEntityUpdateTest.TestEntity.class,
+				CompositEntityUpdateTest.TestEntityEmbed.class,
+		}
+)
+@ServiceRegistry(
+		settings = {
+				// For your own convenience to see generated queries:
+				@Setting(name = AvailableSettings.SHOW_SQL, value = "true"),
+				@Setting(name = AvailableSettings.FORMAT_SQL, value = "true"),
+				// @Setting( name = AvailableSettings.GENERATE_STATISTICS, value = "true" ),
+		}
+)
+@SessionFactory
+@Jira("HHH-18721")
+public class CompositEntityUpdateTest {
+
+	@Test
+	void hhh18721TestIdClass(SessionFactoryScope scope) {
+		scope.inTransaction( em -> {
+			TestEntity e = new TestEntity("yyy", "foo");
+			em.persist(e);
+			em.flush();
+			assertTrue(em.contains(e));
+			assertEquals(e.getData(), "foo");
+
+			e.updateData("bar");
+			em.flush();
+			assertEquals(e.getData(), "bar");
+		} );
+	}
+
+	@Test
+	void hhh18721TestEmbedded(SessionFactoryScope scope) {
+		scope.inTransaction( em -> {
+			TestEntityEmbed e = new TestEntityEmbed("yyy", "foo");
+			em.persist(e);
+			em.flush();
+			assertTrue(em.contains(e));
+			assertEquals(e.getData(), "foo");
+
+			e.updateData("bar");
+			em.flush();
+			assertEquals(e.getData(), "bar");
+		} );
+	}
+
+	/**
+	 * Composite primary key class for oid and datum
+	 */
+	public static class TimeScalePkOidDatum implements Serializable {
+
+		@Serial
+		private static final long serialVersionUID = 1L;
+
+		private String oid;
+		private Instant datum;
+
+		public TimeScalePkOidDatum() {
+			// Default constructor
+		}
+
+		public TimeScalePkOidDatum(String oid, Instant datum) {
+			this.oid = oid;
+			this.datum = datum;
+		}
+
+		public String oid() {
+			return this.oid;
+		}
+
+		public Instant datum() {
+			return this.datum;
+		}
+	}
+
+	@Embeddable
+	public static class TimeScalePkOidDatumEmbed implements Serializable {
+
+		@Serial
+		private static final long serialVersionUID = 1L;
+
+		private String oid;
+		private Instant datum;
+
+		public TimeScalePkOidDatumEmbed() {
+			// Default constructor
+		}
+
+		public TimeScalePkOidDatumEmbed(String oid, Instant datum) {
+			this.oid = oid;
+			this.datum = datum;
+		}
+
+		public String oid() {
+			return this.oid;
+		}
+
+		public Instant datum() {
+			return this.datum;
+		}
+	}
+
+	@Entity
+	@IdClass(TimeScalePkOidDatum.class)
+	public static class TestEntity {
+
+		@Id
+		@Column(length = 32, nullable = false)
+		private String oid = null;
+
+		@Id
+		@Column(columnDefinition = "TIMESTAMP WITH TIME ZONE", nullable = false)
+		private Instant datum;
+
+		private String data;
+
+		protected TestEntity() {
+			// For JPA
+		}
+
+		public TestEntity(String oid, String data) {
+			this.oid = oid;
+			this.datum = Instant.now();
+			this.data = data;
+		}
+
+		public Instant getDatum() {
+			return datum;
+		}
+
+		public String getData() {
+			return data;
+		}
+
+		public void updateData(String data) {
+			this.data = data;
+		}
+
+		public String getOid() {
+			return oid;
+		}
+	}
+
+	@Entity
+	public static class TestEntityEmbed {
+
+		@Id
+		@Embedded
+		private TimeScalePkOidDatumEmbed id;
+
+		private String data;
+
+		protected TestEntityEmbed() {
+			// For JPA
+		}
+
+		public TestEntityEmbed(String oid, String data) {
+			this.id = new TimeScalePkOidDatumEmbed(oid, Instant.now());
+			this.data = data;
+		}
+
+		public Instant getDatum() {
+			return id.datum();
+		}
+
+		public String getData() {
+			return data;
+		}
+
+		public void updateData(String data) {
+			this.data = data;
+		}
+
+		public String getOid() {
+			return id.oid();
+		}
+	}
+
+}