This is actually not a bug - what’s happening is that Asana is in the process of updating the My Tasks view to a new format. Because Asana has so many users, it’s taking a few months to transition all workspaces to the new format. In your case, Workspace A is in the new format; Workspace B is not yet. But it ultimately will be and then it will work like Workspace A does.
You can read about this transition and new format here: