I'm having the exact same problem with tannings coming out of my wood. I bought 1 piece of bogwood & 2 pieces of driftwood for my new tank which I set up a couple of days ago.
My water looks a more of a greeny colour, but when I soaked them before putting into the tank (for about 2 hours only) the water went brown.
I have since done a 75% water change, and put the wood in my sons large plastic toy box to soak again!! I introduce boiling water twice a day.
My pieces are a good 10 inches long & 4 inches high.
I hate the colour in my tank personally, seriously considering not bothering with these wood pieces...