[JENKINS-26781] Reproduced problem in test.

Besides failing in master, it also fails in 4e0af43 (merge of #1443), but passes in the 1.598-SNAPSHOT parent 239caf8.
(cherry picked from commit 3304190)

test/src/test/java/hudson/model/DescriptorTest.java

@@ -24,14 +24,25 @@
 
 package hudson.model;
 
+import hudson.Launcher;
 import hudson.model.Descriptor.PropertyType;
+import hudson.tasks.BuildStepDescriptor;
+import hudson.tasks.Builder;
 import hudson.tasks.Shell;
+import java.io.IOException;
+import java.util.List;
+import jenkins.model.Jenkins;
+import net.sf.json.JSONObject;
 import static org.junit.Assert.*;
+import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.JenkinsRule;
+import org.jvnet.hudson.test.TestExtension;
+import org.kohsuke.stapler.StaplerRequest;
 
+@SuppressWarnings({"unchecked", "rawtypes"})
 public class DescriptorTest {
 
     public @Rule JenkinsRule rule = new JenkinsRule();
@@ -51,4 +62,58 @@
         }
     }
 
+    @Ignore("TODO currently fails: after first configRoundtrip, builders list is empty because in newInstancesFromHeteroList $class is BuilderImpl (like stapler-class), kind=builder-a is ignored, and so d is null")
+    @Issue("JENKINS-26781")
+    @Test public void overriddenId() throws Exception {
+        FreeStyleProject p = rule.createFreeStyleProject();
+        p.getBuildersList().add(new BuilderImpl("builder-a"));
+        rule.configRoundtrip(p);
+        List<Builder> builders = p.getBuildersList();
+        assertEquals(1, builders.size());
+        assertEquals(BuilderImpl.class, builders.get(0).getClass());
+        assertEquals("builder-a", ((BuilderImpl) builders.get(0)).id);
+        rule.assertLogContains("running builder-a", rule.buildAndAssertSuccess(p));
+        p.getBuildersList().replace(new BuilderImpl("builder-b"));
+        rule.configRoundtrip(p);
+        builders = p.getBuildersList();
+        assertEquals(1, builders.size());
+        assertEquals(BuilderImpl.class, builders.get(0).getClass());
+        assertEquals("builder-b", ((BuilderImpl) builders.get(0)).id);
+        rule.assertLogContains("running builder-b", rule.buildAndAssertSuccess(p));
+    }
+    private static final class BuilderImpl extends Builder {
+        private final String id;
+        BuilderImpl(String id) {
+            this.id = id;
+        }
+        @Override public boolean perform(AbstractBuild<?,?> build, Launcher launcher, BuildListener listener) throws InterruptedException, IOException {
+            listener.getLogger().println("running " + getDescriptor().getId());
+            return true;
+        }
+        @Override public Descriptor<Builder> getDescriptor() {
+            return (Descriptor<Builder>) Jenkins.getInstance().getDescriptorByName(id);
+        }
+    }
+    private static final class DescriptorImpl extends BuildStepDescriptor<Builder> {
+        private final String id;
+        DescriptorImpl(String id) {
+            super(BuilderImpl.class);
+            this.id = id;
+        }
+        @Override public String getId() {
+            return id;
+        }
+        @Override public Builder newInstance(StaplerRequest req, JSONObject formData) throws Descriptor.FormException {
+            return new BuilderImpl(id);
+        }
+        @Override public String getDisplayName() {
+            return id;
+        }
+        @Override public boolean isApplicable(Class<? extends AbstractProject> jobType) {
+            return true;
+        }
+    }
+    @TestExtension("overriddenId") public static final BuildStepDescriptor<Builder> builderA = new DescriptorImpl("builder-a");
+    @TestExtension("overriddenId") public static final BuildStepDescriptor<Builder> builderB = new DescriptorImpl("builder-b");
+
 }