sphinx inconsistent result - sphinx

Question

have some weird problems with sphinx.
Here's the query log:
[Mon Jan 31 05:43:21.362 2011] 0.158 sec [any/0/ext 511 (0,2000)] [_file] superman
[Mon Jan 31 05:43:51.739 2011] 0.143 sec [any/0/ext 952 (0,2000)] [_file] superman
[Mon Jan 31 05:44:22.042 2011] 0.003 sec [any/0/ext 952 (0,2000)] [_file] superman
[Mon Jan 31 05:44:52.313 2011] 0.003 sec [any/0/ext 952 (0,2000)] [_file] superman
[Mon Jan 31 05:45:22.553 2011] 0.003 sec [any/0/ext 952 (0,2000)] [_file] superman
If you see, the result returned is 511 for the first time, then 952 (the correct result) for the rest. I've tried searching with different result and all seems to be the same.
Some observation:
1) If there's less than 511, the result returned is always correct. It's only when the result is > 511 and less than the max that it is wrong.
2) If there are more result than the max, the returned result will be max (correct).
3) The rest of the results are usually correct, up until the sphinx db re-indexed. Then we'll get 511 again.
Tried it on different sphinx installation, getting the same result.
my client code:
$cl->setServer("localhost", 3312);
$cl->setMaxQueryTime(10);
$cl->SetLimits(0, 2000, 2000);
$cl->setMatchMode(SPH_MATCH_ANY);
call_user_func_array(array($cl, 'setSortMode'), array(SPH_SORT_EXTENDED, '#id DESC'));
$result = $cl->query('superman', '_file');
sphinx.conf:
index download_file
{
source = file
path = /disk1/data/sphinx/file
morphology = stem_en
enable_star=1
min_word_len = 3
min_prefix_len = 0
min_infix_len = 3
}
searchd
{
max_matches = 100000
port = 3312
log = /var/log/searchd/searchd.log
query_log = /var/log/searchd/query.log
pid_file = /var/log/searchd/searchd.pid
}
indexer
{
max_iops = 40
mem_limit = 128M
}