Currently if you approach a keep, and begin to damage a wall it does not set the keep on fire, this allows a small group of people to move ahead of time, and siege a wall that may not be commonly approached before a bg enters and bypasses the outer wall. I was not able to gather a screenshot of this issue unfortunately.
I am unable to provide a source on the issue, so it is possible this was the intended mechanic on live. If you would like me to gather more information regarding this please let me know and I will attempt to gather more.
Warmap Keep Flame Issue
Re: Warmap Keep Flame Issue
Thank you for your report. This will be resolved by next patch.