Description of problem:
Bash script memory utilization continually increases if bash internal pattern matching / substitution is used.

Version-Release number of selected component (if applicable):
[root@RHEL6-TEST mkandoll]# rpm -qi bash
Name        : bash                         Relocations: (not relocatable)
Version     : 4.1.2                             Vendor: Red Hat, Inc.
Release     : 33.el6_7.1                    Build Date: Mon 17 Aug 2015 03:51:51
Install Date: Fri 25 Mar 2016 04:26:05 PM MST      Build Host: x86-027.build.eng
Group       : System Environment/Shells     Source RPM: bash-4.1.2-33.el6_7.1.sr
Size        : 3142151                          License: GPLv3+
Signature   : RSA/8, Thu 20 Aug 2015 08:01:55 AM MST, Key ID 199e2f91fd431d51
Packager    : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
URL         : http://www.gnu.org/software/bash
Summary     : The GNU Bourne Again shell


How reproducible:
Every time

Steps to Reproduce:
Reproduced using script:
[root@RHEL6-BASIC mkandoll]# cat test17.sh
#!/bin/bash

while /bin/true
do

        test="something1234"
        test=${test//[^a-zA-Z0-9_.]/}

done

Run script for some time using:
nohup ./test17.sh 2>&1 > /dev/null &

Watch using top.

Actual results:
Memory usage increases without bound.

Expected results:
Memory is allocated first time and saved for reuse later.

Additional info:
Reproduced on a test vm using Red Hat Enterprise Linux Server release 6.5 (Santiago) that I upgraded bash package to 33.el6_7.1.  Seeing this in production servers running Red Hat Enterprise Linux Server release 6.7 (Santiago).
Testing is not possible on production servers.

For a workaround I am rewriting scripts that utilize this specific substitution to use echo piped to tr.