Observed one crash in gcbasher on 64 bit OS X with the following message:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error ([...]/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp:766), pid=51303, tid=15363
# assert(PSParallelCompact::mark_bitmap()->is_marked(addr)) failed: not marked
#
# JRE version: Java(TM) SE Runtime Environment (7.0_40-b30) (build 1.7.0_40-ea-b30)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.0-b51-internal-201306250825.thomas.8016740-fastdebug mixed mode bsd-amd64 compressed oops)
# Core dump written. Default location: /cores/core or core.51303
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#

vm_info: Java HotSpot(TM) 64-Bit Server VM (24.0-b51-internal-201306250825.thomas.8016740-fastdebug) for bsd-amd64 JRE (1.7.0), built on Jun 25 2013 04:42:40 by "jprtadm" with gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)

ILW: HLH (crash, low occurence, no workaround known) -> P2 until further investigated