NFA showing double the volume/rate of expected data for interfaces with WCCP enabled.
Any version of NFA.
Cisco devices with WCCP enabled on Netflow interfaces.
There are several Cisco defects for various IOS versions that cause doublt the amount of Netflow to be sent from the device, including defects CSCsb21972 and CSCts49162
Contact Cisco Support to see if there is a patch or workaround for your device/IOS or disable WCCP on that interface.