Digital Link III input problem

Hi! Regards from Poland. I have a technical problem with Digital Link III, I am using and will mainly use Coax / Optical inputs. But I noticed that DLIII after switching on, it incorrectly activated the USB input while working with the Coax connected streamer. And Surprisingly, on the Coax pług on to DLIII, there was a sound on USB input, but it stops for a fraction of a second.
After manually switching to Coax, it sounds perfect, but I can still manually turn on the USB input, which should be silent - and it sounds as described. After trying with the Optical cable, such a situation does not take place.
Trial with two different Coax cables gave the same results. Any idea?