I'm not sure if this is by design but logically it shouldn't be designed in this way. Please explain the reasoning behind it if it's by design.

Only one of the task lists (Master Specs) in the below screenshot has tasks in it so this issue isn't related with the task list not having actual tasks in it.

The first list is always losing this button after reordering the task lists. The button only appears when the first task list has actual tasks in it.