`cylc dump` still showing more than just `n=0` tasks

[hjoliver]

Test case:

[scheduling]
    [[graph]]
        R1 = "foo => bar"
[runtime]
    [[foo]]
        script = false
    [[bar]]

When this stalls with 1/foo failed, manually trigger 1/bar - which will succeed and leave the task pool.

After this, cylc dump shows 1/bar as present in n=0 even though it is not there (it will be at n=1 relative to the incomplete failed 1/foo):

$ cylc dump -t --flows bug          
bar, 1, succeeded, not-held, not-queued, not-runahead, [1]  # <------ 
foo, 1, failed, not-held, not-queued, not-runahead, [1]

I can confirm that 1/bar is not actually in the pool by trying to remove it:

INFO - Command "remove_tasks" received. ID=49c118ba-2252-4eaa-b4d0-326916a39e57
    remove_tasks(tasks=['1/bar'])
WARNING - No active tasks matching: 1/bar  # <-------