ksh command substitution does not work after stdout/stderr closed

Issue

• User has a tool which after fork() and before execv() call closes the stdout and stderr file descriptors. This causes the execved script written in ksh not working. This behavior can be reproduced by the following simple command:

# ksh -c 'a=`cd;pwd`;echo $a>/tmp/a' >&-;cat /tmp/a

• On RHEL 6.3 or RHEL 5.10, the command results in the output

# ksh -c 'a=`cd;pwd`;echo $a>/tmp/a' >&-;cat /tmp/a
/root
#

However, on RHEL 6.5, it outputs an empty line.