  We study the $D^+ \to \bar K^0 \pi^+ \eta$ reaction where the $a_0(980)$
excitation plays a dominant role. We consider mechanisms of external and
internal emission at the quark level, hadronize the $q \bar q$ components into
two mesons and allow these mesons to undergo final state interaction where the
$a_0(980)$ state is generated. While the $a_0(980)$ production is the dominant
term, we also find other terms in the reaction that interfere with this
production mode and, through interference with it, lead to a shape of the
$a_0(980)$ significantly different from the one observed in other experiments,
with an apparently much larger width.
