Sent mail not saved in sent items

I have an IMAP account that I access from multiple devices. On my Windows 7
desktop running WLM, my sent messages are not being saved in Sent Items
(either on the desktop or on the IMAP server). I have verified that the
"save copy of sent messages in the 'Sent Items' folder" box is checked, and
I have tried using both "Sent" and "Sent Items" in the store special folders
option.

Messages from my Windows Mobile phone are going into the Sent Items folder
on the IMAP server and are then being downloaded to WLM, so I don't think
it's a server issue ... I think there's something wrong with WLM. I'm using
build 14.0.8089.0726.

Any suggestions?

David