Distortion correction rotates image

[Joaquim Sanctorum]

Hi everyone,

For my master's thesis I am using XMAlab software to undistort my (X-ray) images, so they are fit for further analysis. However, the distortion correction has a strange effect on my images that I don't fully understand. 

When I compare the Original images of the grid to the undistorted images of the grid, the undistorted images seem to be rotated. For camera 2, this effect can be clearly observed (right panel in image 'Undistorted grid.png'). This causes problems for my further analysis, since the application of the undistortion to the images I want to use, also rotates (and rescales) these images. 

I will send some images attached to this message, so you can see what I mean.

I wonder if someone also encoutered this problem, and if a solution already exists.

Thanks in advance.

Kind regards,
Joaquim