Thanks for the question. This is a limitation of the way in which the arrays are calculated when using Clipping paths with Extend X/Y Size to area. To create the final geometry, RailClone creates a new array for each spline area, and then all the clipping operations are applied as the final step. So for your pavements RailClone is creating two arrays as shown below.
But as you can see, unfortunately in this case Array 2 is inside Array 1, which explains why you get the doubling of geometry in that area. If you look at the splines being used by the other generator, you can see why this doesn't share the same problem:
There are more individual areas in this example, but none overlap so there's no doubling of geometry.
To fix the pavement you have two options. You can either detach the spline that's causing the problem, clone the RailClone object and apply it to the detached spline separately; or alternatively you could turn off Extend X/Y Size to Area, create an array that covers the entire area and just use the spline as a clipping path. You can see the second solution in the attached file.
I hope that helps, please let me know if you have further questions.