Could be yahoo playing up? They seriously seem to have lost the plot recently. I can see yahoo dying a death in the near future.
I have the same problem with my UK stocks all the time. Sometimes yahoo tells me the stock quotes have changed to different identifiers (when all other sites say no). Then suddenly it says they have reverted back. And 60% of the time, it will not show updated prices for all of the stocks.
I don't know why Apple chose Yahoo for these services.