It's possible your dw hadn't dried out. Like firewood, dw needs to be seasoned before use. If you dry it off, and maybe do a bleach dip to kill anything still living on it, you can probably let it sit in a cabinet or some other out-of-the-way spot for the next several months (hopefully without any odor).
The mopani I've used has come from PetSmart in the reptile section, and has all seemed to be nice and seasoned, and needed only a few hours of boiling before use. No noticeable leeching. I really like the patterns in mopani, so make sure you don't just trash it. Either dry it out and use later, or give it to somebody.