A user whose username contains an _ cannot use tools such as jps. Existing code assumes that it can derive the username from a filename such as /tmp/hsperfdata_noddy by taking everything from the last _ onwards. So if your username is big_ears it will incorrectly reduce /tmp/hsperfdata_big_ears to "ears". The end result is that jps shows the pid but lists "process information unavailable" next to it. jconsole doesn't show the app at all.
It's a dup of 6301562.