[horde] ActiveSync mail sync works only once

[Javier]

Hello,

I've successfully installed a Horde setup in my ISP (Dreamhost).
Everything seems to work, including ActiveSync, except that mail seems
to be synced only once. That is, when I first sync a new device, mail
is fetched normally. However, on any posterior syncs, no new mail is
received, nor is mail deleted using the Horde web interface propagated
to the device.

The workaround is to remove the device from the Horde ActiveSync
devices list, which "resets" it so that it works.... during exactly
one extra sync, at which point it stops working again.

This only happens with mail, calendar works great. I've also tried
with many different EAS clients (Outlook, WindowsMail, Maemo/Meego
devices) and they all show the same problem.

I'm using the current stable versions of Horde, e.g. 5.1.6 and
Horde_ActiveSync 2.16.1 .

Does anyone have any idea what could be causing this? I've perused the
debug logs but cannot find anything interesting, other than
Horde_ActiveSync really seems to believe there are no server-side
changes from the last sync.

May this be because of the IMAP server Dreamhost is using (Dovecot)?

Is there any additional logging I can enable to try to debug this?