I was working on a command block project on my friends server that required right/left click detecting. Since that's not vanilla we had to look up fancy things and nothing was working so we got to this video. https://www.youtube.com/watch?v=533aHg1aTmI It's horribly short but it's 1.8 and seemed to work so we tried the command given. http://pastebin.com/c3R19Ct6 We tried it in an impulse command block and were both immediately kicked with the attached kick message. The server didn't crash but rejoining was impossible so we loaded a backup world. We powered the command block in 15w35e but updated the server to 15w36c and still couldn't join.