I was riding my gelding after lots of off and on rides for about the last several months with 2 other geldings. One horse was dead quiet and mine was on the buckle and the third was was quiet at that time. For the first time in 11 years that I have owned him, he has never lunged at another horse in a defensive position with me on him. First of all I learned from that move that you can fall off at a walk, second thing is that as he ages he get more herd bound in that on the cross ties he was very busy, and the last thing is that he needs a lot more work on the ground for me to be the leader of the 2 of us! We did this last May and he was trying to be the leader and it took me 2 days to sort us out! I am also not very strong mentally or physically right now and he know it!
Bottom line is that you can come off at the walk and never let your guard down and get too comfortable as they can end up on the ground at a walk!