I have a problem with mono/poly arpeggiator and I hope that someone could give me a hint what could be wrong.

When I set arpeggiator in latch mode and select Poly for key assing mode, oscilators won't play one by one. Instead, all the oscilators play at same time even the LED that indicates what oscilator is playing, lites one by one.

Any ideas what could be wrong  

BR, Tero