A continuation of -
Since we are moving to 10.3, I thought I'd re-post the discussion to keep it current with the 10.3 release. Unfortunately, at this time the error on bundle move is still occurring when the cache service is in use or under load. Although the 10.3 release is thus far proving to be more efficient and responsive this error still occurs. Overwriting cache services has stabilized however with the re-inclusion of the 'Keep Existing Cache' parameter at overwrite, and overall communication between the desktop and the server directories is much improved, at least on our network.
In general, (because I can allow my basemaps to be offline for a couple hours each week or each month) I have adopted a modified strategy where I stop the service, set the service to private (Admin role access), start the service, and begin caching - all via python scripts run through task scheduler.
I think I prefer this to my previous method of storing both a private service and cache and a public service and cache, then caching to private, stopping the site, and overwriting the bundles via an OS xcopy.
Hopefully esri will keep trying to solve this issue!