This is intriguing to me, as driftwood normally serves to LOWER pH. So, the fact that the pH spiked when the wood was added means that there is something more going on here than the presence of the wood alone.
Perhaps the wood was soaked in a salt of some sort...
Did you soak the wood before adding it to your tank? I'd suggest giving the wood a good rinse... then a long soak, then change the water the wood is soaking in, and soak it again. Check the pH of the water the wood is in and see if there is a change like in the tank (being a smaller volume of water, it will likely show up rather quickly). Eventually, if the wood has minerals soaked into it, that should leach out during this rinsing and soaking process... and not cause a problem for you in the future.
Incidentally, its always a good idea to presoak any wood being added to the tank before hand, just to be safe.