1. Get a running version of 4.7 with latest 1.4 code. load generated data (this is IMPORTANT), also make sure db is 4.1 (not sure what happens in 4.0)
2. do a simple search for adam, works
3. do an empty search, does not work
4. i spent quite a few hours tracking it down, and finally figured out the cause. Enable mysql query logging if possible.
4a. check mysql query log for UPDATE sessions entry and notice that after the POST the session is quite large and written properly, but after the GET the session seems to be cleared
4b. The problem being in drupal/includes/session.inc, sess_read( ), the session variable seems to be cut off at the utf-8 character <81> which leads to a corrupt sessions and hence session is empty and hence no results
4c.not sure whether it is drupal or mysql or the settings code. i can let u know more details over IM