WAL segments (names) not in a sequence

A PostgreSQL user recently reported on pgsql-admin about an issue:
when he changed wal_level from 'minimal' to 'hot_standby', the WAL
segment sequence rewound, that is, it started using old names. A
snippet of his "ls -lrt pg_xlog":

-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000B3
-rw------- 1 postgres postgres 16777216 May 21 12:13 00000001000000100000000A
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000036
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000008
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000F6
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000E4
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000F2
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000003
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000D5
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000A9
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000D6
-rw------- 1 postgres postgres 16777216 May 21 12:13 00000001000000100000004E
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000D8
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000B4
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000BA
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000000F000000C3
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000071
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000047
-rw------- 1 postgres postgres 16777216 May 21 12:13 000000010000001000000026

# WAL after wal_level changed from 'minimal' to 'hot_standby'

-rw------- 1 postgres postgres 16777216 May 21 12:27 000000010000000E0000007B
-rw------- 1 postgres postgres 16777216 May 21 12:35 000000010000000E0000007C
-rw------- 1 postgres postgres 276 May 21 12:35
000000010000000E0000007C.00000020.backup
-rw------- 1 postgres postgres 16777216 May 21 14:53 000000010000000E0000007D
-rw------- 1 postgres postgres 16777216 May 21 14:53 000000010000000E0000007E
-rw------- 1 postgres postgres 16777216 May 21 14:53 000000010000000E0000007F
-rw------- 1 postgres postgres 16777216 May 21 14:53 000000010000000E00000080

Is this a known issue?

--
Amit Langote