My 11mth old flatcoat has a couple of times now run at top speed away from me during a walk, I'm sure on both occasions he thought he had left me behind.  This morning met 4 other walkers and dogs and walked along with them talking for a bit while dogs played, then with no warning he took off back towards the car at full tilt.  I tried calling and whistling but ended up walking back to the car and met him returning again delighted to find me and I was greatly relieved to.

His hearing seems fine usually, has any-one else had this problem?

I think in his panic to find me he looses his hearing.

My rotti X has done it twice now, in the same place - I take her and my dobe to a little nature park, and they both dash off into the undergrowth chasing small furry things.  Where she has done it, she is chasing squirrels - I tend to keep going, and she'll catch up, but twice she has come back to the trail and gone the wrong way in a panic.  That area tends to distort noise a bit though, so it can sound like my voice is not where it really is!

Have you had his hearing tested?  It may be that he seems alright, but has some sort of bilateral hearing problem (i.e. one ear hears worse or is deaf) - I have the same thing, very slightly deaf in my left ear, but it had to be tested for to pick it up.

Another thought, what was the weather like?  gusty weather can carry sounds away, he may have thought you'd gone when you hadn't.