2D FFT of an image shows some invalid values for high frequencies

Question

I uploaded my 2D FFT magnitude image here:

If you take a look at it, for high frequencies[right, left, top and bottom], only at around x and y-axis, there are some points with high power[yellow color]. These points shouldn't be in the resultant FFT2, since I know the original height image is isotropic and therefore the 2D FFT must look something like the example below(just note high frequencies):

Now, the question is, what could be the possible reasons for such behavior at high frequencies?

added: Here is the magnitude power spectrum before windowing:

https://dl.dropboxusercontent.com/u/82779497/nowin.png

here is the original image, which is a height profile recorded by a profilometer: https://dl.dropboxusercontent.com/u/82779497/asph5.jpg

By the way, I export data as a .txt file from profilometer software to Matlab.