Can't split a polysurface

Hi, I’m trying to split a closed polysurface but I am having an unexpected result. I’m trying to split the surface into 2 pieces using a polyline. When I run split, I am prompted by rhino for the object to split (so I select it and press enter). Next, I select the cutting object (and press enter). I’d expect to now have two separate shells, but rather I get a prompt that says: Creating meshes…2 polysurfaces added to the selection. So the object does not split, if I select it the whole object is selected. Now if I run edge analyze, it tells me that I now have 4 naked edges and no non-manifold edges. BTW - the 4 naked edges are at the position where I would have expected my object to have been split. The upshot is that I can’t seem to split this object and I don’t know why. The object is reported as valid prior to the splitting process and after, so I am not sure why this isn’t working. Any ideas?



Was the polysurface part of a group? If so the net result would be two separate objects that you can’t separately pick until you ungroup them.

OMG - it turns out that somehow the object had become part of a group (although how that happened is unclear). Thank you so much Jim for solving this problem… I was going bonkers!