Full text search ts_heading strange result

I am beginning to use the full text search facilities in Postgresql
(9.0) and find the result of this query a bit strange:

query:

SELECT ts_headline('simple',title, to_tsquery('kerkreg|(church & polity)'))
from akb_articles A
where A.tsv@@ 'kerkreg|(church & polity)'

Result

"Kerkvereniging en <b>Kerkreg</b>: Geskiedenis, beginsel en praktyk.(<b>Church</b> unity and <b>church</b> polity: History, principle and practice.)"

Why is 'polity' not highlighted?

Regards
Johann

--
Johann Spies Telefoon: 021-808 4699
Databestuurder / Data manager

Sentrum vir Navorsing oor Evaluasie, Wetenskap en Tegnologie
Centre for Research on Evaluation, Science and Technology
Universiteit Stellenbosch.

"Look not every man on his own things, but every man
also on the things of others." Philippians 2:4
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