diff --git a/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/main/java/org/springframework/boot/configurationmetadata/SimpleConfigurationMetadataRepository.java b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/main/java/org/springframework/boot/configurationmetadata/SimpleConfigurationMetadataRepository.java
index 5becb4d6906d..1d9a2553495e 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/main/java/org/springframework/boot/configurationmetadata/SimpleConfigurationMetadataRepository.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/main/java/org/springframework/boot/configurationmetadata/SimpleConfigurationMetadataRepository.java
@@ -117,4 +117,17 @@ private <V> void putIfAbsent(Map<String, V> map, String key, V value) {
 		}
 	}
 
+/*
+Uncomment this code to fix issue revealed by ConfigurationMetadataRepositoryJsonBuilderTests#severalRepositoriesIdenticalGroups3()
+
+	private void putIfAbsent(Map<String, ConfigurationMetadataSource> sources, String name,
+			ConfigurationMetadataSource source) {
+		ConfigurationMetadataSource existing = sources.get(name);
+		if (existing == null) {
+			sources.put(name, source);
+		} else {
+			source.getProperties().forEach((k, v) -> putIfAbsent(existing.getProperties(), k, v));
+		}
+	}
+*/
 }
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/java/org/springframework/boot/configurationmetadata/ConfigurationMetadataRepositoryJsonBuilderTests.java b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/java/org/springframework/boot/configurationmetadata/ConfigurationMetadataRepositoryJsonBuilderTests.java
index 0706b9036d17..b22da1be4708 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/java/org/springframework/boot/configurationmetadata/ConfigurationMetadataRepositoryJsonBuilderTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/java/org/springframework/boot/configurationmetadata/ConfigurationMetadataRepositoryJsonBuilderTests.java
@@ -113,6 +113,102 @@ void severalRepositoriesIdenticalGroups() throws IOException {
 		}
 	}
 
+	
+	/*
+	 * A rewrite of severalRepositoriesIdenticalGroups() using "containsOnlyKeys" to show actual vs. expected when assert fails.
+	 */
+	@Test
+	void severalRepositoriesIdenticalGroups_rewritten() throws IOException {
+		try (InputStream foo = getInputStreamFor("foo")) {
+			try (InputStream foo2 = getInputStreamFor("foo2")) {
+				ConfigurationMetadataRepository repo = ConfigurationMetadataRepositoryJsonBuilder.create(foo, foo2)
+						.build();
+				
+				// assert all properties are found
+				assertThat(repo.getAllProperties()).containsOnlyKeys(
+						"spring.foo.name", 
+						"spring.foo.description", 
+						"spring.foo.counter", 
+						"spring.foo.enabled", 
+						"spring.foo.type");
+				
+				// we have a single group containing all properties
+				assertThat(repo.getAllGroups()).containsOnlyKeys("spring.foo");
+				
+				ConfigurationMetadataGroup group = repo.getAllGroups().get("spring.foo");
+				assertThat(group.getProperties()).containsOnlyKeys(
+						"spring.foo.name", 
+						"spring.foo.description", 
+						"spring.foo.counter", 
+						"spring.foo.enabled", 
+						"spring.foo.type");
+				
+				// the group contains 3 different sources
+				assertThat(group.getSources()).containsOnlyKeys(
+						"org.acme.Foo", "org.acme.Foo2", "org.springframework.boot.FooProperties");
+				
+				assertThat(group.getSources().get("org.acme.Foo").getProperties()).containsOnlyKeys(
+						"spring.foo.name",
+						"spring.foo.description");
+				
+				assertThat(group.getSources().get("org.acme.Foo2").getProperties()).containsOnlyKeys(
+						"spring.foo.enabled",
+						"spring.foo.type");
+				
+				assertThat(group.getSources().get("org.springframework.boot.FooProperties").getProperties()).containsOnlyKeys(
+						"spring.foo.name",
+						"spring.foo.counter");
+			}
+		}
+	}
+	
+	/*
+	 * "foo3" contains the same properties as "foo2" except they refer to a group that already exists in 
+	 * "foo1" (same NAME, same TYPE).
+	 * 
+	 * This test shows that the union of properties collected from the sources is less than what the group actually 
+	 * contains (some properties are missing).
+	 */
+	@Test
+	void severalRepositoriesIdenticalGroups3() throws IOException {
+		try (InputStream foo = getInputStreamFor("foo")) {
+			try (InputStream foo3 = getInputStreamFor("foo3")) {
+				ConfigurationMetadataRepository repo = ConfigurationMetadataRepositoryJsonBuilder.create(foo, foo3)
+						.build();
+				
+				assertThat(repo.getAllProperties()).containsOnlyKeys(
+						"spring.foo.name", 
+						"spring.foo.description", 
+						"spring.foo.counter", 
+						"spring.foo.enabled", 
+						"spring.foo.type");
+				
+				assertThat(repo.getAllGroups()).containsOnlyKeys("spring.foo");
+				
+				ConfigurationMetadataGroup group = repo.getAllGroups().get("spring.foo");
+				assertThat(group.getProperties()).containsOnlyKeys(
+						"spring.foo.name", 
+						"spring.foo.description", 
+						"spring.foo.counter", 
+						"spring.foo.enabled", 
+						"spring.foo.type");
+				
+				
+				assertThat(group.getSources()).containsOnlyKeys("org.acme.Foo", "org.springframework.boot.FooProperties");
+				assertThat(group.getSources().get("org.acme.Foo").getProperties()).containsOnlyKeys(
+						"spring.foo.name",
+						"spring.foo.description",
+						"spring.foo.enabled",		// <-- missing although present in repo.getAllProperties()
+						"spring.foo.type");			// <-- missing although present in repo.getAllProperties()
+				
+				assertThat(group.getSources().get("org.springframework.boot.FooProperties").getProperties()).containsOnlyKeys(
+						"spring.foo.name",
+						"spring.foo.counter");
+			}
+		}
+	}
+	
+	
 	@Test
 	void emptyGroups() throws IOException {
 		try (InputStream in = getInputStreamFor("empty-groups")) {
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/resources/metadata/configuration-metadata-foo3.json b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/resources/metadata/configuration-metadata-foo3.json
new file mode 100644
index 000000000000..417cf5d613ed
--- /dev/null
+++ b/spring-boot-project/spring-boot-tools/spring-boot-configuration-metadata/src/test/resources/metadata/configuration-metadata-foo3.json
@@ -0,0 +1,23 @@
+{
+  "groups": [
+    {
+      "name": "spring.foo",
+      "type": "org.acme.Foo",
+      "sourceType": "org.acme.config.FooApp",
+      "sourceMethod": "foo2()",
+      "description": "This is Foo."
+    }
+  ],
+  "properties": [
+    {
+      "name": "spring.foo.enabled",
+      "type": "java.lang.Boolean",
+      "sourceType": "org.acme.Foo"
+    },
+    {
+      "name": "spring.foo.type",
+      "type": "java.lang.String",
+      "sourceType": "org.acme.Foo"
+    }
+  ]
+}
\ No newline at end of file