umounting md backed jail filesystems - busy

[Ian Downes]

> > $  jls
> > JID  IP Address      Hostname                      Path
> 
> What does jls -d say? i.e. is the jail really shutdown or is it still dieing?

Thanks, indeed jls -d does show the jail as in the process of dying. I
watched jls -d and (unscientifically) as soon as jls -d reported the jail was
completely dead I was able to umount and destroy the filesystem. 

I hadn't expected it to take a minute or more for a jail to die. Is this usual?
Can anyone suggest what may be causing this? Perhaps a network related timeout?

thanks,

Ian