Standby server witching into master role after import failure

Hi folks,

I've got an issue I'm currently investigating and I'm not 100 sure about
the root cause.
The setup is pretty easy: A standby server via PITR is importing
WAL-files from master server. During this import it appears there has
been an error which cause the standby to finish the importing and going
live. I'm copying in LOG-file pars I tried to translate to English
(server running de_DE)

< 2011-09-28 19:38:26 CEST >LOG: unexpected page address 8B/5A000000
at logfile 144, Segment 1, Offset 0
< 2011-09-28 19:38:26 CEST >LOG: Redo done by 90/1EB48
< 2011-09-28 19:38:26 CEST >LOG: last completed transaction was
at logtime 2011-09-28 19:37:04.605199+02
< 2011-09-28 19:38:26 CEST >LOG: Logdatei 000000010000009000000000
recovered from achive
< 2011-09-28 19:39:26 CEST >LOG: choosen new Timeline-ID: 2
< 2011-09-28 19:40:26 CEST >LOG: Recover from archive finished

Obviously there have been an issue on WAL-file. But any chance to get
any detail what went wrong and what can be done to prevent such things
in future?

It's all 8.4 running on SLES11 SP1 AMD64

Cheers,
Frank