  The COMPASS experiment at the CERN SPS features good charged particle
tracking and coverage by electromagnetic calorimetry, and our data provide
excellent opportunity for simultaneous observation of new states in two
different decay modes within the same experiment. The existence of the
spin-exotic $\pi_1(1600)$ resonance in the $\rho\pi$ decay channel is studied
for the first time in COMPASS in both decay modes of the diffractively produced
$(3\pi)^{-}$ system: $\pi^{-}p \rightarrow \pi^{-}\pi^{0}\pi^{0}p$ and
$\pi^{-}p \rightarrow \pi^{-}\pi^{+}\pi^{-}p$. A preliminary partial-wave
analysis (PWA) performed on the 2008 proton target data allows for a first
conclusive comparison of both $(3\pi)^{-}$ decay modes not only for main waves
but also for small ones, including the spin-exotic $1^{-+}$ wave. We find the
neutral versus charged mode results in good agreement with expectations from
isospin symmetry. Both, the intensities and the relative phases to well-known
resonances, are consistent for the neutral and the charged decay modes of the
$(3\pi)^{-}$ system. The status on the search for the spin-exotic $\pi_1(1600)$
resonance produced on a proton target is discussed.
