Account Lockout Policies

I recently came across a problem in our environment where the account lockout policy was not applying to Domain accounts. After reading up on the some of the questions posted here on TechNet I found that another administrator who had created the original account lockout gpo and linked it to an OU which apparently makes the policy apply in a way where it only affects local accounts.

So I went back and unlinked the gpo and modified the account lockout policy in Default Domain Policy however I am still finding that it is not applying to domain accounts. Have I missed something? 

Server 2008 R2 Enterprise

Clients running Windows 7/Windows 8.1

Account Lockout Specifies: 

Duration 15 Minutes

Threshold 5 Invalid attempts

Reset Lockout Counter 15 Minutes

Thanks!