Btree index left link changed unexpectedly after bringing up 8.3.11 warm standby

I'm seeing this on a Pitrtools managed warm standby box that we
periodically bring the db fully up on in order to test if the standby is
good.

After the standby is up, then a db wide VACUUM produces:

2010-10-28 17:20:51 NZDT WARNING:  relation "node" page 248500 is
uninitialized --- fixing
2010-10-28 17:20:51 NZDT WARNING:  relation "node" page 248502 is
uninitialized --- fixing
2010-10-28 17:20:51 NZDT WARNING:  relation "node" page 248504 is
uninitialized --- fixing
2010-10-28 17:20:54 NZDT ERROR:  left link changed unexpectedly in block
21042 of index "content_node_node_type_id_inserted_idx"

I'm guessing the index error is due to the uninitialized table pages
(the index "content_node_node_type_id_inserted_idx" is on the "node"
table). Are the uninitialized pages cause for concern, or merely an
artifact of log shipping?

The is 8.3.11 on Debian Lenny x86-64.

Thanks

Mark