When I try to create a split line feature using a surface intersection, I get an error 99% of the time. Almost every time it says, "cannot create an edge which does not split a face". Occasionally it says "trim tool and target are not intersecting....blah blah" even though they most definitely are.

I have to add 3-4 features to work around this every time, which is unacceptable. I use my workaround 4-5 times daily, at a minimum.

I had this problem about 25% of the time in 2008, and it has gotten worse since then. I cannot recall if this has ever worked in 2009. I am on 2009 sp 2.1.

What bugs the most is that one may clearly see that the surface is fully intersecting, but SW can't figure it out.

After some testing, I have narrowed this bug down to 1 case: when both the tool and target surfaces have more than one face, split fails every time. If either tool or target is a single face body, the split will work. Otherwise, one must select one face on the target body per split feature, which is cumbersome and inefficient. Since very few of my surfaces have only one face, this bug bites me every time I need a surface split.

I attached some images for this, as well as a sample part file with some arbitrary surfaces. Try to split the multi-face pair, and tell me what happens!