My guess is that it's a bug created by the changes made to improve performance in 1.8, they aren't rendering the Dragon unless you look at it therefore the bar isn't rendered unless you look at the Dragon .
Nevertheless, the issue was spotted on our side, though it is very silly that the client would render additional experience bars if given a experience percentage over 100.
FVbico, correct me if I'm wrong, but the server sending packets for rendering entities is completely different from the client displaying the exp bar. The server can't tell the client, "add another experience bar off-centered", this is a graphical bug client-side, the experiencing is displayed properly until level 101 is reached. Then the 101->102 bar is displayed off centered, and upon reaching 102, the bar is correct again.
It's silly that corrupt packets crash the client and could easily be fixed on Mojang's side.
Bukkit is a server-mod, not client side. I'm reporting a client side issue.
Why would this be invalid if it is obviously a graphical issue client-side?
@Squawkers13 For the case of plugin/server use, the Action Bar fulfills only some aspects that the boss bar does. The Boss Bar is exceptionally handy for displaying timers, countdowns, as well as other visual things. The Action Bar strictly displays text and isn't a valid replacement, more a counterpart. Also, this is not just a Server/Plugin issue, the dragon fight is now awkward without the Dragon's health displaying unless the player is facing the dragon.