According to my tests, this problem happens with any input, not only nested Generators. I can reproduce it using a simple Segment.
It is caused by a change in the logic of No-slice Segments. With RC3, segments can be extended beyond the spline's end, but RC4 removes them.
I modifed the code a bit to fix it, and seems to work well. If there are not problems (we must do more tests), the fix will be included in the next update.