I was just messing around trying to interface Node.JS to gnugo GTP and bumped into this when I ran boardsize 9 on a board that was already started:
(;GM[1]FF[4]SZ[9]KM[0.0]HA[0]GN[GNU Go 3.8 stepped on a bug] ;W[ae];B[dd];B[aa]
) gnugo 3.8 (seed 1331613819): You stepped on a bug. Please mail this message, including the debug output above, to address@hidden