I have seen a problem somewhat like what you describe. Except it was on a Cincinnati machine(custom post). We finally found that the main problem was when the machine was trying to make extremely small arcs. In the post, there are two lines you would need to check. That is, if the post for the Fadal is anything like that of the Cincinnati one. Here is what we found:
arccheck : 1 # Check for small arcs, convert to linear
ltol : .050 # Length tolerance for arccheck
The first line was already set to 1 (Yes) but the second line was small. I can't remember exactly what it was, but it was less than .005 I believe. The way I figure, is that the second line checks to see how long the arc is, and if it is under .050 in this example, it converts it to linear. After changing that, the problems went away.
Sorry for digging up an old post.