Found a interesting one when activating my Server 2012 R2 KMS host with the KMS key.
All was going well and got as far as the commiting the changes when the following error popped up and it is rather strange
Despite the error text the commit was not successful and your configuration changes have not been saved
Turns out to be a rather simple fix. On the commit page for some reason the wizard defaults to 0 as the KMS TCP Listening port number. For KMS this should be 1688 changing this port number to 1688 resolves the error and allows the configuration to be saved.