*ist DS -- black frames. A fault?

Anyone else experienced this?

Sometimes (about one time in 20) when my much-loved *ist DS has been off or in standby for a while, and I then wake it up and take a shot... the image comes out black.

Subsequent images come out fine.

Doesn't seem to be a power thing, because it happens with fresh LiIon batteries as well as rechargeables.

And yes, I *have* taken the lens cap off!

Will probably take it back to shop (still under guarantee) but it's very hard to repeat the problem on demand. Pointers appreciated.

I've certainly never experienced this in 12 months. Sounds like a fault to me.