BUG: Surface topology gets heavily changed after split operation

On rare occasions I figure out that Rhino tends to replace simple original surfaces that usually have degree 1 in one direction with some kind of a rectangular patch surface instead.
This just happened again and I think that this bug it must be investigated further, because it could lead to losing the initial surfaces used to build the more complex models.

One of my surfaces changed after I split it with with a couple of G2 blend edge surfaces on the top and bottom, and a G1 fillet surface on the right side (I used the ! _Split _Pause _Curve command each time). Originally, the surface in question was a straight extrusion made via the Gumball’s extrusion handle with degree 3 in one direction and degree 1 in the opposite direction. However, after I split it I found that its topology got totally wrong. Very strange. I was lucky to keep copies of my initial surfaces into a back-up layer just in case.

I just used a copy of the original surface and tried to recreate the bug, but it does not happen again.

I will send a portion of the model on tech@mcneel.com

Hi Bobi - I have your file, thanks - so far (quick try) I cannot repeat this however…


Thanks for the update, Pascal! Tomorrow I will spend some time to try to split the edges of that surface in different order to see if that is what causes the bug. :slight_smile: