  The 2-m robotic Liverpool Telescope (LT) reacted promptly to the
high-redshift (z=4.048) gamma-ray burst GRB 060206. The afterglow was
identified automatically and multicolor r'i'z' imaging was triggered without
human intervention. Combining our data with those obtained from later
follow-ups provides a well-sampled optical light-curve from 5 minutes to >2d
after the gamma event. The light-curve is highly structured with at least three
bumps evident in the first 75 minutes, including a major rebrightening
(Delta_r'=-1.6 at t=3000s), interpreted as late energy injection. At early time
(t=440s), we find evidence for fast (Delta t_(rest)<4s<<t) variability,
indicating on-going internal-engine activity. We emphasise that a low redshift
GRB (z<1) with similar intrinsic properties would have been interpreted
completely differently due to undersampling of the light curve in the rest
frame at early times; the light-curve behaviour of GRB 060206 should therefore
not be considered peculiar. Finally, although the observed late-time steepening
of the optical light curve resembles a jet break if taken in isolation, the
lack of a corresponding change in the X-ray slope rules out a jet-break
interpretation. Traditionally, GRB jet breaks have been inferred from optical
data in the absence of simultaneous X-ray data. We suggest therefore that
current estimates of the jet opening angle distribution might be biased by
events like GRB060206. Consequently, the GRB explosion energy distribution and
event rates may have to be revised.
