[MNG-7634] Revert MNG-5982 and MNG-7417

This closes #917

Author: michael-o

maven-resolver-provider/src/main/java/org/apache/maven/repository/internal/DefaultArtifactDescriptorReader.java

@@ -274,8 +274,11 @@ private Model loadPom( RepositorySystemSession session, ArtifactDescriptorReques
                 modelRequest.setValidationLevel( ModelBuildingRequest.VALIDATION_LEVEL_MINIMAL );
                 modelRequest.setProcessPlugins( false );
                 modelRequest.setTwoPhaseBuilding( false );
-                modelRequest.setSystemProperties( toProperties( session.getSystemProperties() ) );
-                modelRequest.setUserProperties( toProperties( session.getUserProperties() ) );
+                // This merge is on purpose because otherwise user properties would override model
+                // properties in dependencies the user does not know. See MNG-7563 for details.
+                modelRequest.setSystemProperties(
+                        toProperties( session.getUserProperties(), session.getSystemProperties() ) );
+                modelRequest.setUserProperties( new Properties() );
                 modelRequest.setModelCache( DefaultModelCache.newInstance( session ) );
                 modelRequest.setModelResolver( new DefaultModelResolver( session, trace.newChild( modelRequest ),
                                                                          request.getRequestContext(), artifactResolver,
@@ -328,10 +331,17 @@ private Model loadPom( RepositorySystemSession session, ArtifactDescriptorReques
         }
     }
 
-    private Properties toProperties( Map<String, String> map )
+    private Properties toProperties( Map<String, String> dominant, Map<String, String> recessive )
     {
         Properties props = new Properties();
-        props.putAll( map );
+        if ( recessive != null )
+        {
+            props.putAll( recessive );
+        }
+        if ( dominant != null )
+        {
+            props.putAll( dominant );
+        }
         return props;
     }