I think that's common. The recoil upsets your position. Using that spray adhesive might help.
My problem with standing relates to my sleeping habits. I spent the last ten years on second shift and I can't seem to wake up. The first relay causes me to be sleepy, shaky and a bad disposition. I've noticed that it takes a week for my body to get on the early shift so I can shoot a match. I shoot with country types that are up at 5 AM. I have an IDPA match this weekend and I was up until two yesterday. Since I help to run the match, I can delay my shooting all the way until 10:00.
I glue the rifle to me, and glue myself to the shooting mat. At Camp Perry, some of the kids entertain themselves by spraying that stuff on the toilet seats. Bad news especially for those with a (formerly) hairy arse.
Regards
J.R.