When there is a 'normal' audio track listed in the Playing Tracks panel, but it is unavailable because it was e.g. deleted from the drive, there will be an exclamation mark beside it explaining the problem.
But when the same happens for a podcast episode, there is no exclamation mark but the text is displayed in a different (disabled) colour.
I think it would be better if the behaviour with podcasts was the same as for normal tracks.