Log message " last_statrequest ... is later than collector's time" - what does it mean?

Hi,

I upgraded our test database from PostgreSQL 8.4.8 to 9.0.4 via pg_dumpall.
The database seems to work fine, but now the logfile of the new database is
flooded with log messages like these:

2011-09-16 13:48:32 CEST: LOG: database system was shut down at 2011-09-16
13:48:29 CEST
2011-09-16 13:48:32 CEST: LOG: autovacuum launcher started
2011-09-16 13:48:32 CEST: LOG: database system is ready to accept
connections
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.614476+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.626524+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.638498+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.650502+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.662507+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.674506+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.686507+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.698498+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.710517+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.722504+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.734495+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.746498+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.758503+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.770501+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.782509+02
2011-09-16 13:48:54 CEST: LOG: last_statrequest 2011-09-16
13:48:55.890743+02 is later than collector's time 2011-09-16
13:48:54.794496+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.500691+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.51259+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.524583+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.536605+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.548601+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.560569+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.572571+02
2011-09-16 13:49:07 CEST: LOG: last_statrequest 2011-09-16
13:49:08.176573+02 is later than collector's time 2011-09-16
13:49:07.584579+02

Configuration:
- SUSE Linux Enterprise Server 10 (i586)
- uname -a: Linux 2.6.16.21-0.8-bigsmp #1 SMP Mon Jul 3 18:25:39 UTC 2006
i686 athlon i386 GNU/Linux
- PostgreSQL 9.0.4, installed with RPM: postgresql-9.0.4-54.5

What do these messages mean and what can I do to avoid them?

Cheers,
Stephan