The reason the surface is rebuilt from 0,0 is because when you initialize a Syphon Server Obj-C object it as a NSSize struct that is NSZeroSized, and will only init the texture when you first call publishFrameBlahBlah, because it needs to make a texture to match.
If your scene size is changing at all, then a rebuild is triggered, because textures cannot be resized, only destroyed and re-created anew at a different size.