Users are missing data

So really the failing to sync can lead to the failing to drag and move items
For the failing to sync, really you should look at the client logs (you will have to enable Virtual Vault logging as well) and find the error there, you may also have something on the EV Server under "Symantec Enterprise Vault" event logs

For the dragging and dropping issue, i have seen this quite a few times when the OST does not download or sync the hidden message correctly, if you go to C:\Program Files\Microsoft\Office12\ you should see a program called ScanOST.exe, run that and enable automatic fixing of errors, that usually fixes those issues.

But really you don't want to move too much or push to much in to the VV until you have your synchronization issues sorted out.