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