Different output when setting usesCPUOnly=Yes/No

I convert a tensorflow model to mlmodel and test it on iphone6. When I set MLPredictionOptions.usesCPUOnly to NO, the output is same as expected, it is same with tensorflow's output and tfcoreml's. But when I set it to YES, the output is quite different from usesCPUOnly. Could anyone give any suggestion? is it a bug of CoreML?


My mtmodel parameters:

Inputs: Image(Color 128x128)

Outputs: MultiArray(Double 1 x 128 x 128)

mtmodel size: 125KB


Thanks in advance.