Custom index structure and strange count problem

Hi *,
during the last few months I've been building a new index structure as part of a research project.
Everything seems to work properly, however I have some strange issues with the count sql command.
I introduced some custom structures (mainly document and hybrid_query) with which my index access method is supposed to
work.
There is an operator "&&" which is supposed to use my index structure (what also works properly).
The function that maps to the operator "&&" is called hybrid_index_query, which I use to compare my results given from
theindex with the real results that are supposed to appear in the final result set. 
Having described the outer circumstances (in a very short way), I will now show the strange stuff that happens:

test=# select id from documents where hybrid_index_query(to_document(words, points), row('radio pleas news'::tsvector,
'[(-90,-180),(90,180)]')) order by id; id   
------2137215121682207220822092210221122662296
(10 rows)

This query takes a sequential scan and works properly (returning 10 rows).

test=# select id from documents where to_document(words, points) && row('pleas radio news'::tsvector,
'[(-90,-180),(90,180)]')order by id; id   
------2137215121682207220822092210221122662296
(10 rows)

This query uses my index structure and returns the same result as in the sequential scan above.
Until here, everything seems to work fine. However, if I issue the same queries using the count aggregate function in
SQL,there are some odd results: 
test=# select count(*) from documents where hybrid_index_query(to_document(words, points), row('radio pleas
news'::tsvector,'[(-90,-180),(90, 180)]'));count  
-------   10
(1 row)

Using the sequential scan, still, everything seems fine.
However, if I now do the index scan (my function will be called 11 times, returning false at the end), I get the
followingresult: 
test=# select count(*) from documents where to_document(words, points) && row('pleas radio news'::tsvector,
'[(-90,-180),(90,180)]');count 
-------    7
(1 row)

This seems strange, because the same query returned 10 rows (when I didn't use the aggregate). If I issue queries that
countthe id column, I receive the following: 
test=# select count(id) from documents where hybrid_index_query(to_document(words, points), row('radio pleas
news'::tsvector,'[(-90,-180),(90, 180)]'));count  
-------   10
(1 row)

test=# select count(id) from documents where to_document(words, points) && row('pleas radio news'::tsvector,
'[(-90,-180),(90,180)]');count 
-------   10
(1 row)

These two queries do again return the same results.
Thus, I don't know, what's wrong here, does anybody know about that behaviour, or is it my fault that the results are
wrong,somehow? 
Thanks in advance

Carsten Kropf