Breaking Minecraft physics

Recently on a good server I go on occasionally (6r36, awesome server) I Built a tower to world height ,hell knows why, and dug a hole to bedrock level then did the old trick of putting up a sign and some water three blocks high to stop me from getting hurt...now this was bizzare because when i jumped of i made it and it was awesome but....I was damaged, and in all honesty I thought Minecraft physics denied the fact that could happen, and i know this isn't much to talk off and was probably a mishap, but has anyone else tried this?