The removed comment mentions this, but here's why this is a difficult mess:
- In window A, view a board with "Group by: Owner" and no tasks owned by "Alice". Since "Alice" owns no tasks, this means the columns do not have an "Assigned to: Alice" header!
- In window B, edit task T and assign it to Alice.
- In window A, press "R".
Window A now not only needs to update to properly reflect the state of task T, it actually needs to draw a new "Assigned to: Alice" header in every column.
Fortunately, the "group by" code anticipates this being a big mess, is fairly careful about handling it, and the client can handle this state change and the actual code change here isn't too involved. This is just causing a lot of not-very-obvious indirect effects in the pipeline to handle these situations that need complex redraws.