Help index isn't updated fast enough ????

In an application I use an subset condition on a dbase table to filter the
records. This is used in a multi user environment with a windows NT server.
Somehow sometimes users can acces records wich are outside the subset
condition?? When this happens, most of the times the record has just been
changed by another user so that after that it should be removed from the
index. Could it be somekind of caching so that the index isn 't updated
yet???
I am using a dBase index on the table defined in database desktop
with in the subset condition (filter) expression filled with pog <1 where
pog is a integer field.