  The isospin-breaking decay eta {\to} 3pi is an ideal tool to extract
information on light quark mass ratios from experiment. For a precise
determination, however, a detailed description of the Dalitz plot distribution
is necessary. In that respect, in particular the slope parameter alpha of the
neutral decay channel causes some concern, since the one-loop prediction from
chiral perturbation theory misses the experimental value substantially. We use
the modified non-relativistic effective field-theory, a dedicated framework to
analyze final-state interactions beyond one loop including isospin-breaking
corrections, to extract charged and neutral Dalitz plot parameters. Matching to
chiral perturbation theory at next-to-leading order, we find alpha = -0.025 +-
0.005, in marginal agreement with experimental findings. We derive a relation
between charged and neutral decay parameters that points towards a significant
tension between the most recent KLOE measurements of these observables.
