Strange FFT Output

I've done a few simulations using $fwrite to capture the data, both in Natural and Bit Reversed orders, and the output is still incorrect. I've attached an example output at the bottom. The input for both of these examples is a 17.36Hz sine wave, generated in the Verilog testbench.

I know it's not a problem with the FFT engine, as running the testbench that is generated with the core gives exactly the same output as when run in Matlab. One thing I realised I was doing wrong previously, was using an unsigned integer as the input, something which I have now rectified.