To my understanding of the API documentation on Creep.reserveController reserving a controller should prevent other players from claiming it: ""Temporarily block a neutral controller from claiming by other players...".

I'm relatively new to the game and wasn't aware of this when I tried to claim my 2nd room (first ever claimController call) when I leveled to GCL 2. I was able to claim someone's reserved controller despite it having 4400+ ticks on the reservation clock.

Link to replay: http://screeps.com/s/YrCznx

Now I don't mind, since it saved me a bunch of waiting. But it wasn't entirely clear to me whether this is intended behavior or not. After discussing with others on Slack > help, they advised me to post this as a potential bug.