diff -r a93a9eda13f7 -r 5cbac8938c4c src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Fri Jul 16 21:33:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Jul 19 11:06:34 2010 -0700
@@ -638,6 +638,11 @@
 
     // Now retry the allocation.
     if (_cur_alloc_region != NULL) {
+      if (allocated_young_region != NULL) {
+        // We need to ensure that the store to top does not
+        // float above the setting of the young type.
+        OrderAccess::storestore();
+      }
       res = _cur_alloc_region->allocate(word_size);
     }
   }