One of Igor's JPRT submissions hit this assertion failure:

[GC pause (young) 183M->87M(221M), 0.1608904 secs]
[GC pause (young) 185M->91M(221M), 0.2777634 secs]
[GC pause (young) 181M->97M(221M), 0.1786966 secs]
[GC pause (young) 183M->102M(221M), 0.1913175 secs]
[GC pause (young) 181M->108M(221M), 0.1928595 secs]
[GC pause (young) 180M->114M(221M), 0.1890257 secs]
[GC pause (young) 181M->120M(221M), 0.1939025 secs]
[GC pause (young) 181M->127M(221M), 0.1923573 secs]
[GC pause (young) 181M->133M(221M), 0.1976771 secs]
[GC pause (young) (initial-mark)[GC concurrent-mark-start]
181M->139M(221M), 0.2008953 secs]
[GC concurrent-mark-end, 0.3158352 sec]
[GC remark, 0.0072940 secs]
[GC concurrent-count-start]
[GC concurrent-count-end, 0.3820240]
[GC cleanup 161M->125M(221M), 0.0106024 secs]
[GC concurrent-cleanup-start]
[GC concurrent-cleanup-end, 0.0075199]
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (g1RemSet.cpp:887), pid=25527, tid=23
# Error: guarantee(!r->is_young(),"It was evicted in the current minor cycle.")
#
# JRE version: 7.0-b50
# Java VM: OpenJDK Server VM (15.0-b02-2009-03-16-074947.iv159533.hotspot-gc mixed mode solaris-sparc )
# An error report file with more information is saved as:
# /opt/jprt/products/T3/jbb/hs_err_pid25527.log
#
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#
Abort - core dumped

We've only seen this once (so far at least), despite a few more JPRT submissions since.