See JDK-8208468. Although this CR was addressed by removing the println from the debuggee, it does not address the real problem. When a debuggee does a println, the output can be broken up and interspersed with multiple jdb output lines. As an example, taken from JDK-8208468, the debuggee was doing the following:

 System.out.println("Arguments but no locals");

And the jdb output contained:

Sending command: cont
receiveReply: FAILED
reply[0]: > Argument
reply[1]: Breakpoint hit: s b"thread=main", nsk.jdb.locals.locals002.locals002a.allKindsOfLocals(), line=100 bci=62
reply[2]: ut n100 System.out.println("Locals but no arguments"); // locals002.BREAKPOINT_LINE2
reply[3]:
reply[4]: o lmain[1] ocals

Note in this case we were initially at a breakpoint set on the println, and when the user did a "cont", the output for hitting the next breakpoint got intermixed with the println. The odd thing is that it seems that this intermixing happens at the character level.