login page reloading after a successfull login

[Russell Stuart]

I've just got roundcube "running" on Debian Squeeze.  I can log in successfully, and it displays my messages.  But a few seconds later it reloads the login page without me touching anything.

session.auto_start = 0 in php.ini.

There are no errors in any logs, no messages are displayed by the browser.  Stuff does appear in its sqlite database in the session table, but the "vars" column is blank.

Can anyone give me a hint on where to start looking?