src/java.base/share/classes/java/util/stream/StreamSpliterators.java

*** 187,196 ****
--- 187,198 ----
          @Override
          public Spliterator<P_OUT> trySplit() {
              if (isParallel && !finished) {
                  init();
  
+                 if (buffer != null && buffer.count() > 0) // partial traversal started
+                     return null;
                  Spliterator<P_IN> split = spliterator.trySplit();
                  return (split == null) ? null : wrap(split);
              }
              else
                  return null;