Here the short/overload is in the unit itself. Most probably the phones output stage, precisely one of the many opamps in it, malfunctions. For technical reasons this issue does NOT cause DC at the output (the other, still working opamps prevent this), but causes current overload within the unit. The IEM output stil works because it is a separated output circuitry (obviously).
Unfortunately sometimes electronic parts just die, for no obvious reason. And the more units are sold the more often you can read about it in forums. Still our return and repair rate is very low, otherwise we could not keep the price at where it is right now.
Thanks, that explanation is very much appreciated. The unit sounded great until the failure.