CMS: assert((HeapWord*)nextChunk <= _limit) failed: sweep invariant

The nightly test:

runtime/ParallelClassLoading/std_CLs/URLClassLoader/forName/inner-complex

failed with the following assert:

;; Using jvm: "C:/local/common/jdk/baseline/windows-i586/jre/bin/server/jvm.dll"

Warning: This error log is *not* generated by the following JVM:
           C:/local/common/jdk/baseline/windows-i586/jre/bin/server/jvm.dll
         
         Expected vm_info: [Java HotSpot(TM) Server VM (20.0-b04-internal-201012161759.ysr.gc-merge-fastdebug) for windows-x86 JRE (1.7.0), built on Dec 16 2010 15:09:41 by "jprtadm" with unknown MS VC++:1600]
         Actual vm_info: []
         
         JVM symbol lookup may be incorrect.
         Please use --jvm=<path/to/jvm> to point to the correct JVM.
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (C:\temp\jprt\P1\B\175901.ysr\source\src\share\vm\gc_implementation\concurrentMarkSweep\concurrentMarkSweepGeneration.cpp:8110), pid=21568, tid=17992
# assert((HeapWord*)nextChunk <= _limit) failed: sweep invariant
#
# JRE version: 7.0-b121
# Java VM: Java HotSpot(TM) Server VM (20.0-b04-internal-201012161759.ysr.gc-merge-fastdebug mixed mode windows-x86 )
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#

Stack trace:

--------------- T H R E A D ---------------

Current thread (0x00ae3400): ConcurrentGCThread [stack: 0x00bc0000,0x00c10000] [id=17992]

Stack: [0x00bc0000,0x00c10000], sp=0x00c0f9e4, free space=318k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
Warning: This error log is *not* generated by the following JVM:
           C:/local/common/jdk/baseline/windows-i586/jre/bin/server/jvm.dll
         JVM symbol lookup may be incorrect.
         Please use --jvm=<path/to/jvm> to point to the correct JVM.

V [jvm.dll+0x25862a];; ?report_and_die@VMError@@QAEXXZ+0x54a
V [jvm.dll+0x250be5];; ?report_vm_error@@YAXPBDH00@Z+0x45
V [jvm.dll+0x335f8c];; ?doAlreadyFreeChunk@SweepClosure@@AAEXPAVFreeChunk@@@Z+0x17c
V [jvm.dll+0x339a72];; ?do_blk_careful@SweepClosure@@UAEIPAVHeapWord@@@Z+0xa2
V [jvm.dll+0x32226e];; ?blk_iterate_careful@CompactibleFreeListSpace@@QAEXPAVBlkClosureCareful@@@Z+0x2e
V [jvm.dll+0x33481f];; ?sweepWork@CMSCollector@@AAEXPAVConcurrentMarkSweepGeneration@@_N@Z+0x15f
V [jvm.dll+0x338f72];; ?sweep@CMSCollector@@QAEX_N@Z+0x312
V [jvm.dll+0x33e8a3];; ?collect_in_background@CMSCollector@@QAEX_N@Z+0x4c3
V [jvm.dll+0x34125a];; ?run@ConcurrentMarkSweepThread@@UAEXXZ+0x28a
C [msvcr100.dll+0x5c6de]
C [msvcr100.dll+0x5c788]
C [kernel32.dll+0x4d0e9]
C [ntdll.dll+0x419bb]
C [ntdll.dll+0x4198e]

Current thread is:

=>0x00ae3400 (exited) ConcurrentGCThread [stack: 0x00bc0000,0x00c10000] [id=17992]

Heap:

Heap
 def new generation total 14784K, used 7603K [0x04d00000, 0x05d00000, 0x05d00000)
  eden space 13184K, 55% used [0x04d00000, 0x05417578, 0x059e0000)
  from space 1600K, 21% used [0x059e0000, 0x05a35820, 0x05b70000)
  to space 1600K, 0% used [0x05b70000, 0x05b70000, 0x05d00000)
 concurrent mark-sweep generation total 49152K, used 227K [0x05d00000, 0x08d00000, 0x0ad00000)
 concurrent-mark-sweep perm gen total 36080K, used 20662K [0x0ad00000, 0x0d03c000, 0x0ed00000)
runtime/ParallelClassLoading/std_CLs/PrivateMLet/forName/anonymous-complex

http://sqeweb.sfbay.sun.com/nfs/results/vm/gtee/JDK7/NIGHTLY/VM/2010-12-25/GC_Baseline-Xconc/vm/linux-i586/server/mixed/linux-i586_vm_server_mixed_vm.parallel_class_loading.testlist/analysis.html