strange problem with Sent folder

[fchassaing]

Hi,
I have a strange problem with one of my user (and only this one so far).
I've search thru the forum, but it is hard to find something on that topic.
I've migrated his mail as for everybody else using imapsync.
In his Sent Folder the column "To" always contains his own email address as if it was a "From" column.
Now what is strange is that if I make this column disappear an re-appear (using right-clik on the column's bar) the selected message (and only this one) now displays the correct 'To' address.
Of course this display update is not retained beween logins...
If tried to reload the Sent folder by emptying it and redo the imapsync step, but nothing changed.
Let me add that this happens both in IE and FF (so it is not browser related)
Does anyone already experienced such strange behaviour ?
may I file a bug and if yes how to word that ?
thanks