The 2-2 is misleading. For one thing, Bonner has only played 30+ minutes in 3 games this year, and Spurs are 2-1 in those. Those 2 wins were Orlando at home and Milwaukee on the road - and Bonner was INSTRUMENTAL in both those victories.
The loss was @Boston - arguably SAS' more difficult contest of the season thus far. The King of +/- was +13 in that game, so it's impossible to say that he was responsible for the tough loss.
He played 29:56 in the loss against LAC - which you may be rounding up for the second loss. He was flat out awful in that game...but so were Duncan, McDyess, Blair, and Splitter (Bonner actually led all bigs in rebounds).