I don't know that SPM will actually generate an origin outside of the FOV, but it will load and view such a volume (even without the .mat file). The control panel displays the origin as being outside the FOV. This can easily happen when you're not acquiring full-brain images.
I can understand the problem you have with trying to parse the originator field. I'll go ahead and modify the way I create the analyze file prior to running to3d so as to assure that the origin is at the center of the volume.
thanks
doug