  The quasi-one-dimensional S=1 Heisenberg antiferromagnet with a biquadratic
term is investigated at zero temperature by quantum Monte Carlo simulation. As
the magnitude of the inter-chain coupling is increased, the system undergoes a
phase transition from a spontaneously dimerized phase to a N\'eel ordered or
spin nematic phase. The numerical results suggest the possibility of an
unconventional second-order transition in which the symmetry group
characterizing one phase is not a subgroup of the other.
