error writing setting display.applicationTitle, reason: TypeError: data is null (when adding localised application title)

What steps will reproduce the problem?
1. Open Configuration Editor
2. Go to "User Interface" --> Application Title
3. Select a new language code and click "Add locale"
4. An error occurs

What is the expected output? What do you see instead?

The expected output is a new input field. Instead an error message is shown. 

What version of the product are you using? On what operating system?

SVN revision 108, tomcat 6, SLES 11.0
Browsers: 
* Firefox 4.0b11 on Mac OS X 10.6
* Camino Version 2.0.6 (1.9.0.19 2010111021) on Mac OS X 10.6
* Chrome 11.0.672.2 dev

Please provide any additional information below.

This also happens with other localisation fields.

Chrome provides a more detailed message: error writing setting 
display.applicationTitle, reason: TypeError: Cannot read property 'isDefault' 
of null

Original issue reported on code.google.com by menno.pi...@gmail.com on 25 Feb 2011 at 7:47

SpacyNG / pwm

error writing setting display.applicationTitle, reason: TypeError: data is null (when adding localised application title) #38