WAL Sequence

Dear list member:
I have small problem,
below is the output from ls -larth command for listing WAL segments.
As far as my understanding every new WAL segment created is numerically greater than the previous one,but below out show the WAL 13 is created after wal 14,15,16,17,18,19 checked by creation time.

Can anybody please suggest me is ther anything going wrong or am i just doing something silly. :)

OS:Suse 10.3 64 bit,PostgreSQL server:8.2.4

$ ls -alrth
total 129M
-rw------- 1 postgres postgres 269 2008-01-06 23:59 000000010000001700000003.00010588.backup
drwx------ 11 postgres postgres 4.0K 2008-01-06 23:59 ..
-rw------- 1 postgres postgres 16M 2008-01-07 08:59 000000010000001700000014
-rw------- 1 postgres postgres 16M 2008-01-07 09:59 000000010000001700000015
-rw------- 1 postgres postgres 16M 2008-01-07 10:59 000000010000001700000016
-rw------- 1 postgres postgres 16M 2008-01-07 11:59 000000010000001700000017
-rw------- 1 postgres postgres 16M 2008-01-07 12:59 000000010000001700000018
-rw------- 1 postgres postgres 16M 2008-01-07 13:59 000000010000001700000019
-rw------- 1 postgres postgres 16M 2008-01-07 14:59 00000001000000170000001A
drwxr-xr-x 2 postgres postgres 4.0K 2008-01-07 15:09 archive_status
drwxr-xr-x 3 postgres postgres 4.0K 2008-01-07 15:09 .
-rw------- 1 postgres postgres 16M 2008-01-07 15:15 000000010000001700000013

With Regards
Ashish

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