Automute 2nd slice

I am using ver3 and Flex 6600.
Found new feature and looking how to change behaivour.
When i open 2nd slice (slice i can hear the active sliceB, speaker icon on slice A is crossed as disabled. When I click anywhere on slice A, it enables audio on slice A and put crossed red line on a speaker icon of slice B.
It is repeatable.
I can click on dissabled audio icon and it enables a 2nd slice up to the point I click on another spot on active slice, it is getting dissabled again.

I do not recall this behaivour on ver 2.4.9. I could hear both slices without enabling speakers.
What is the setting to ensure both of them active?
I want to disable slice that i want to disable WHEN I NEED IT.
Thanks
Sergey, KN7K