storage sync failed on magnetic disk: Permission denied

When the cluster performs a massive disk operations (like nightly
vacuuming or smth)
I offten got such error in log file:

2005-11-12 14:52:29 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied
2005-11-12 14:52:29 ERROR: storage sync failed on magnetic disk:
Permission denied
2005-11-12 14:52:30 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied
2005-11-12 14:52:30 ERROR: storage sync failed on magnetic disk:
Permission denied
2005-11-12 14:52:31 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied
2005-11-12 14:52:31 ERROR: storage sync failed on magnetic disk:
Permission denied
2005-11-12 14:52:32 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied
2005-11-12 14:52:32 ERROR: storage sync failed on magnetic disk:
Permission denied
2005-11-12 14:52:33 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied
2005-11-12 14:52:33 ERROR: storage sync failed on magnetic disk:
Permission denied
2005-11-12 14:52:34 LOG: could not fsync segment 0 of relation
1663/17735/210608: Permission denied

The error exists for a few minutes then dissapears and cluster works
normally till next time.
(actually next night ;) )
I had this situation few minutes ago on my Windows XP box and tryed to
look what was wrong with this file:
1663/17735/210608
1) File existed
2) It was locked (by somebody ??? ) during the error existance.
3) File dissapeared when the error had dissapered.
4) NTFS Permissions were set correctly.


This error was found on Windows 2000 Server SP4, Windows Proffesional and
a Windows XP HE.
On 8.0.0, 8.0.4 and 8.1 PostgreSQL servers.

Is it a windows bug?
It looked like as if somebody (not postgres) got an exclusive access to
that file.

Sorry about my english