Is futures::executor::block_on documentation about uncompleted spawned tasks up to date?

[vi]

futures::executor::block_on's documentation says "... tasks spawned onto the default executor ... may not complete before the function returns.". But the source code contains this comment:

// run any remainingspawned tasks to completion
    pool.run(&mut exec);

Doesn't running remaining spawned tasks to completion contradict "may not complete"?