Err, because if series doesn't contains() the text "Perry Rhodan", you replace series with " - " -- that also applies if the series is just plain empty...
Try:
Code:
{series:'in_list($, "&", "Perry Rhodan", strcat($, ' - '), $)'|_ | }{series:lookup(Perry Rhodan,,authors)}/{series_index:0>4s| | - }{title} - {authors}