i was in parkour and i was going to go into a parkour course and i thought i saw some one but i pressed tab and it showed only me in parkour , i told my self 'my mind must be playing tricks on me,' but when i was in a parkour course i saw in the chat a message saying (a players name that i will not say because maybe they don't want me to) finished nether_end with 14 deaths in 12:13 mins, i pressed tab again but only i was in parkour.
I'm not sure this is a parkour glitch, but a tab glitch. It happens. If this happens again, do /list or press tab in your chat bar.
Thanks for letting us know. You can use /list to see who else is in your server, as @Mickeyheart said. And, as @GertAlert noted, if you think that you found a glitch, please report those in the Bug Reports forum.