Steps to reproduce:

1. Take a custom field of type Select List (com.atlassian.jira.plugin.system.customfieldtypes:select).
2. Add an option to it that is invalid if parsed as XML. Example:

   <FONT COLOR="#009900">Normal</FONT><img src="/images/icons/priority_minor.gif" >
   

3. Set this option as a value of this custom field to some issue.
4. Open XML view.

Observe: XML fails to be parsed, because the generated XML does not escape the option into CDATA section.

XML looks like

                  <customfield id="customfield_10540" key="com.atlassian.jira.plugin.system.customfieldtypes:select">
                    <customfieldname>[cf]Priority</customfieldname>
                    <customfieldvalues>
                      <customfieldvalue key="10560">
                        <FONT COLOR="#009900">Normal</FONT>
                        <img src="/images/icons/priority_minor.gif">
                      </customfieldvalue>

                    </customfieldvalues>
                  </customfield>

Expected: custom field value is wrapped into CDATA.

Note that "Multi Select" and "Multi Checkboxes" custom fields wrap their values into CDATA.

Reproducible on JIRA 5.0rc1.