I'm finding this same behavior - reading the LSB from the AD719x is unreliable with an Atmel SAM3 device.
Atmel says it is the fault of the AD part - not a long enough hold time after the last rising clock edge.
Support - SPI Data coming from the Analog Devices ADC7194 slave is not sampled correctly by the Atmel SAM3 / SAM4 SPI in…
Either way it is a problem.