I too experience the same, using IC 8.0, and also other problems with "curved stock".
The cut and extend tools are certainly not predictable for radie and circles.
Further, I tried to bevel off two sides of a curved stock using hole blocks. One side ended up correct, but the other hole block did not swing into the right position in the unfold position and hence did not cut as axpected. I get a feeling the two sides of the 2d sheet divided by the X- axis, are not connected or cooperating properly. (I think it's the X-, but could be the Y- axis).
I then tried to cut with a solid block using "cut sheetmetal part", and that gave a proper unfolded shape, but an unusable edge line on the flat shape in the drawing, that cannot be picked for dimensioning.
I also get a tilted display of the unfolded view when the radie crosses the 2d-sheet x-axis.
I'm trying to get a curved lexan windshield ready soon, but this is beginning to get very boring.
Also, there should be a way to edit the curved stock in the unfolded shape, and project this back to the curved shape, as this is how one cuts it, and a straight edge like it's cut or sawed, is easy enough to model on the unfolded shape, but tricky or impossible for IronCad on the curved shape.