Send option cannot switched off

The send option is always active and cannot switched off and the result of this is that I cannot pull the dry/wet knob back, is always adjust at maximum wet reverb. The knob simply is not active.
How can I make this knob “active” ???

I noticed the same thing.
Also the buttons for headphones cannot be turned off
after being activated.

Actually according to @ca-booter, the buttons are always active in one of the four mixes.
If you switch them off in Mix2, they will be off in Mix1.
A strange construction…

Sorry, I mean if you turn them ON in Mix2, they will be set OFF in Mix1. ;^)