Hotsync with evolution loses calendar entries occasionally - any ideas why?

[Chris G <cl isbd net>]

My wife uses a Treo 680 with Evolution on xubuntu 10.04.

She uses both Evolution and the Treo 680 for entering and changing
calender entries, she hotsyncs them fairly regularly but sometimes it
doesn't get done for several days if she's away on business etc.

Most of the time it works fine and everything is synchronized correctly
but occasional items are missed and it's only her good memory that means
that they don't get forgotten.  

For example we recently came back from a short holiday and she hotsynced
the Treo with Evolution.  One item that she had put into the Treo for
8th August didn't appear on Evolution's calendar.  Simply making a
trivial change to the event got it synchronised correctly.

So, two questions:-

    Can anyone suggest a mechanism which might cause events to fail to
    synchronise occasionally?  E.g. would a hotsync *failure* make
    either end think that an item had been synchronised even when it
    hadn't and thus not be sent on the next (successful) hotsync?

    Is there a way to force a full synchronisation both ways so that one
    can be sure that the Treo 680 and Evolution are in step?  I know
    syncevolution has a way of doing this (it calls it a 'slow sync' I
    think).

-- 
Chris Green