Trying to figure out a strange behavior!

Setup as follows:
idr48+T112 as monitor, idr16+T80 as FOH, Dante cards in both idr’s. Everything works great but when I try to send a signal from the idr 16 at FOH to the monitor console something very strange happens.

The T80 has trim on Surface on the idr48 channels sent via Dante but I can not change the gain from the T112 on the channels sent from the idr16 so I need to have PreAmp on Surface on those channels on the T80 to be able to set the gain.

When I change the gain on one of the channels the other channel (not paired or ganged or in any other way connected as far as I can tell) adds 24 db in the trim section. Also as an added bonus to the already confused situation when switching to trim on one channel the other follows.

It does not matter what socket or channels I use, the behavior is the same. It also does not matter if anything is connected to the inputs of the idr16.

Any takers?

Thanks in advance for your knowledge and advice!