'query was cancelled' - depending on search pattern

Hello Bugs,
a query that uses pattern matching like this:
   SELECT .. WHERE  ( (content || authorname) ~* ( '.*gesellschaft.* |
.*wirtschaft.*' ) )

produces an error 'Query was cancelled' - sometimes, depending on the
search words.
Seems quite strange to me, I increased some postgresql.conf parameters,
without effect, and failed in finding anything on 'query was cancelled' in
the docs or in google.

Any hints are welcome (and an update to the docs about error messages would
make sense anyway).
// Bernd vdB