I thought I was hearing things (no pun intended) when I plugged in my headphones and kept on hearing the audio come out of the laptop for a few seconds ..... then after those few seconds, the sound finally came through on the headphones.
Yes, it is annoying.
You'd think for a $3k laptop this machine should not have these types of problems.
Hope the next OS update resolves this.
Same with me. I actually just posted a similar question, and then found yours here! I have a 13" MBP, running the version 10.8.3 (is this Mountain Lion? I'm a new Mac user so don't understand all of these crazy names for OS!) I noticed playing music that I hear it in the speakers still a few seconds after plugging in my headphones, until it finally transfers into the headphones. So strange.