Did the MR in Nov, used international connections. No sticker was placed at FL and in fact was stopped at gate lounge and then asked those silly questions, can't recall being asked of where I started my journey today.
It sure helped to have the return BP printed at AC at DFW, by the agent sharing the first name of a famous but short temper tennis player.
LHR is not my fav MR destination, but sometimes you have to play the cards one is dealt :-)