Switching external user management "on" and then back "off" causes performance issues

Performance degraded and system became unusable when switching external user management "on" and then back "off".

Here is the sequence of steps that can be used to re-produce this:

1) Create osuser.xml for LDAP support

2) Rename the original osuser.xml to osuser.orig

3) Copy LDAP-enabled osuser.xml into directory

4) Go into JIRA and toggle external user management to "on":

Administration --> General Configuration --> External User Management

5) Stop Apache

6) Start Apache

7) Performance is still OK

8) Rename the LDAP-enabled osuser.xml to osuser.ldap

3) Rename osuer.orig to osuser.xml

4) Go into JIRA and toggle external user management to "off":

Administration --> General Configuration --> External User Management

5) Stop Apache

6) Start Apache

7) Performance degrades, nothing loads, and system becomes unusable

8) Re-boot of system doesn't help and toggling Apache doesn't help

9) The only way to recover is to start with a fresh instance of JIRA and to copy the original server.xml and entityengine.xml files back into the new instance, and then restore from a backup.xml file