--- old/test/hotspot/jtreg/vmTestbase/nsk/jdi/ReferenceType/instances/instances003/instances003.java	2018-06-08 19:43:39.135732831 +0200
+++ new/test/hotspot/jtreg/vmTestbase/nsk/jdi/ReferenceType/instances/instances003/instances003.java	2018-06-08 19:43:38.870721333 +0200
@@ -41,6 +41,7 @@
  *         done
  *         Test is executed for following sublcasses of ObjectReference: StringReference, ThreadReference, ClassLoaderReference
  *
+ * @requires vm.gc != "Z"
  * @library /vmTestbase
  *          /test/lib
  * @run driver jdk.test.lib.FileInstaller . .
@@ -125,6 +126,11 @@
             ":" + referrerCount + ":" + referrerType +
             (referrerType.equals(ObjectInstancesManager.WEAK_REFERENCE) ? "|" + ObjectInstancesManager.STRONG_REFERENCE : ""));
 
+        // Note! This test is broken, in the sense that it incorrectly assumes
+        // that no GC can happen before it walks the heap. In practice, it seems
+        // to only affect this test when using ZGC. However, this test will also
+        // fail when using other GCs if an explicit GC is done here.
+
         // the instance counts should not be affected by creating multiple references
         checkDebugeeAnswer_instanceCounts(className, createInstanceCount, objectsToFilter);