"Switch from current encoding to specified encoding not supported editing a CLOB field, (4232576)

I am storing XML in a CLOB field. When I double click on the field to edit it, I get the following error message:
"Switch from current encoding to specified encoding not supported." I hit enter, and then I'm allowed to edit the XML.

I didn't used to get this, and I wanted to see what has been done (options, formatting, etc.) that I will not be prompted with this error message every time I open the field.

Here is a sample of the XML clob field I'm trying:
<?xml version="1.0" encoding="utf-16"?>
<PositionDescriptionForm >
<Header>
<EmployeeID>COV:</EmployeeID>
<FirstName>TIMOTHY</FirstName>
<LastName>MAUNEY</LastName>
</PositionDescriptionForm>

Incompatibility issue with <?xml version="1.0" encoding="utf-16"?>

WORKAROUND:

None

STATUS:

Waiting for fix in a future version of Toad for Oracle.