Sync via mobile deletes Calendar entries

I have a number of HP Ipaq 2750, connecting to Sony ericsson t630 phones via
bluetooth, to pickup emails contacts and diary from our exchange 2000
server.

I have found that if the phone loses connection during a sync that the diary
and contacts are wiped from the exchange server, but remain on the PDA. I
can sync them back from the PDA to the desktop, but is there a way to
prevent this data lose when the phone loses signal.

Any ideas greatly appreciated.