  Understanding the pattern of gluon radiation in $t \bar t$ production
processes is important for making an accurate determination of the top mass
from the measurement of its decay products. In a recent paper we showed that
the exact matrix element and parton shower (HERWIG) calculations gave very
different results for the distribution of gluon jets in $t \bar t$ production
at the Tevatron $p \bar p$ collider. By repeating the calculation for the
simpler $e^+e^- \to b \bar b W^+W^-g$ process, we reveal even more dramatic
differences between the two approaches. We conclude that there are significant
differences in gluon radiation between HERWIG and the matrix element
calculation in regions of phase space where one would expect agreement.
