How can an asset allocation be negative

I'm pretty new to investing, and I'm trying to get a better grasp on what things mean. In this case, I'd like to know how and why the “short-term” assest on one of my Fidelity accounts is -1%? Also, how can an asset be at 101% (“bonds” in this case)?

If it helps, this account is invested solely in FTBFX.