What do you think of this logic as a possible solution:
How about when selecting multiple items in the left hand side list, and when each item is added to the middle list, also initially “select” it in the middle list??? Basically, when an item is initially “added” to the middle pane, set it “selected”.
So that when selecting an additional item and adding items to the “multiple selection list” in the middle pane they are initially selected, which seems to be what people are looking for so they can they do bulk editing and can make changes to multiple items at the same time.
This would remove the extra “click in the middle pane and Select All” step. You could still click in the middle pane to de-select items.
The first item in the middle list is already selected, and the items in the left-hand list are already selected also, so why not make the items in the middle list initially selected???
Just a thought… Since some of us FREQUENTLY forget to “Select All” in the middle pane when doing bulk editing…