massive performance problem with q.setStartAtIndex() and q.setEndAtIndex()

hi there,

i figured out a performance problem with large tables using 
q.setStartAtIndex() and q.setEndAtIndex()
there are more than 100.000 entries in the table and a simple search 
which should return about 90.000 items still takes more than 10(!) seconds.
i am using the index methods to retrieve only 10 datasets per query out 
of these 90.000 total items using an iterator.

when i implement the same query directly as a sql command like:
"SELECT * FROM user WHERE name LIKE '%name%' LIMIT 50000,10"
the query takes less than 1 second ...

am i doing something wrong or is it a bug ?

with best regards,
Björn