The results are:
Fantastyka – dziedzina literatury (a także film u i innych dziedzin sztuki i kultury). Polega ona na kreowaniu istot, które są wytworem ...

Note the "film u" which is probably because of the code "[[film]]u". Expected summary would contain "filmu".

Also note the next result:
Fantastyka w polskiej Wikipedii 130px | left | grafika Poniższa strona to portal dla wikipedystów zainteresowanych ogólnie pojętą ...

Which probably is because of the usage of older name of the file namespace:
[[Grafika:Bryce-demo-May00PicOfMonth.JPG|130px|left|grafika]]

Both bugs seems to be have the same base - I would expect Lucene extension to get get summaries based on the output from the MediWiki parser and as seems it uses some other parsers which seem to be a bit behind the parser.

Version: unspecified
Severity: normal
URL: http://pl.wikipedia.org/w/index.php?title=Specjalna:Szukaj&redirs=1&search=fantastyka&fulltext=Search&ns0=1&ns2=1&ns6=1&ns8=1&ns10=1&ns14=1&ns100=1&title=Specjalna:Szukaj&advanced=1&fulltext=Advanced+search