In my environment, 100% reproducible crash; having cloned hg repository with NetBeans, I am not able to build binaries of tests (test distribution) on JDK 7u40 b28; Invoking Ant target (ant build-test-dist -Dtest.fail.on.error=false) after a while ends up:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x00007fff8983aaf5, pid=870, tid=6403
#
# JRE version: Java(TM) SE Runtime Environment (7.0_40-b28) (build 1.7.0_40-ea-b28)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.0-b47 mixed mode bsd-amd64 compressed oops)
# Problematic frame:
# C [libsystem_c.dylib+0x1af5] memmove$VARIANT$sse42+0xcd
#
# Core dump written. Default location: /cores/core or core.870
#
# An error report file with more information is saved as:
# /Users/tomas/space/core-main/hs_err_pid870.log
Phoning home...
Using server: 10.161.186.18, port 4711
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#
Abort trap: 6 (core dumped)

....looking at stacktraces of crashed thread, in all cases they are the same.
Attaching one error log, and crash log from OS X. Link to coredump is here: http://beetle.cz.oracle.com/data/transfer/tmusil/tmp/CoreDumps/core.870

You can try to reproduce on your environment by doing something like:

#clone netbeans repo
hg clone http://hg.netbeans.org/core-main
cd core-main
# give ant more memory
export ANT_OPTS=-Xmx1024m
# build minimal distribution of netbeans
ant -Dcluster.config=java
# ....and now try to build test distribution; here I see the same crash all the time
ant build-test-dist -Dtest.fail.on.error=false