Thunderbird, leave messages on server

Hello

I configured my pop3 account in Thundirbird to leave messages on server,
for a maximum of 30 days.

That worked fine, but since May 16 (41 days ago), a have no messages
deleted on the server.

Fact is that the last release (1.5.0.4) is dated May 16, 2006; bug in
this release or the update process?

Any Idea?