I've never used it but it could be something hacky Seneca's done as part of his script. Are you using it in 401? I'm not sure he's updated his scripts for the latest version yet - could be a bug introduced there.
I just started using Modo for unwrapping my models. I believe I have the work flow down now, but when I am done unwrapping my models often, but not always, have split edges along the UV seams. So essentially the geometry is no longer connected in 3D space along edges that share a UV seam. I can't figure out what I'm doing…