Any pattern letter using by DateTimeFormatter.dateTimePattern has to be case-sensitive as defined here: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/globalization/Dat eTimeFormatter.html#setDateTimePattern()
The example above won't be work using Flex 4.6 + FlashPlayer 11. For example: The DATE_FORMAT defined within the British locale property file has to be dd/MM/yy (not DD/MM/YY).
The pattern is case sensitive. d and D are different patterns, and upper case Y is not a valid pattern letter. d is for day of the month. D for day of the year. For example if you format a date: Feb 1 2012:
using pattern "dd/MM/yy" you get "01/02/2012"
using pattern "DD/MM/yy" you get "32/02/2012"
I will update the doc.