Always walk with the scorers and check out your targets after shooting... _especially_ in IDPA if the scorer/RO also shoots IPSC. I have caught many instances where IPSC scoring is used in IDPA (e.g. PE for every shot, non-threat hits per round, fail to give FTN, etc.)
I hate it when targets are pasted up befre I had a chance to see it and when its not alpha-alpha or -0. Fortunately this dones't happen much, but it is annoying.