setting time format to 24hr through GP

i am having trouble setting the time to a 24hr clock through group policy.

 -- i open GPM and navigate down to "user configuration/preferences/control panel/regional options"

 -- create an option

 -- on the time tab i change the format to be HH:mm:ss and click ok

i now see in the regional options window the option i created, an order of 1, and in the processing box "Run in user's context" is yes.

the problem is when i open the option up again, the time format say h:mm:ss tt again.  it changes from what i want as soon as i click the ok button.

i am running Win2008 R2

please tell me what could possibly be the issue.