Magical Mystery Event Tour

I have posted before about R12 having some event changes that you need to prepare for, but a good three months in I am still seeing events that are completely new to me.  We had a session that appeared to be stalled and our investigation found the thread was in the "gcs drm freeze in enter server mode" wait event locking against LMON when it was just sitting there in the event "rdbms ipc message".  Oddly enough, the situation just resolved itself but not before I captured another event in the wild that I had never seen before: "latch: object queue header operation".  I am not quite sure what happened here, so this gets tagged as a mystery....until the next time and I can solve it