Is there any change made to the NetApp array? If the array is configured in CFO mode, then it will be detected as an A/PC array type and the only supported load balancing mode is FailOverOnly.
When SmartMove is enabled in 5.1, the initial resynchornization of mirrored volume is also skipped. So you will get what you want by upgrading to SFW 5.1 release.
