I'd like to thank Bernd for his patience in helping me get to the bottom of this mysterious problem. After a couple hours driving my computer via TeamViewer, he finally worked it out, and everything is up and running smoothly with all the new preset/matrix content.
For Corte and anyone else who might have this issue, here's what eventually worked. We're not sure why, but lowering the User Account Control Settings to the lowest setting ("Never notify") from the Control Panel did the trick. For some reason, the files simply weren't being updated with the normal UAC settings. It may be an issue with the Home Edition of Windows 7, or maybe it's just our computers being capricously mischievous - in any case, it's all taken care of here. I hope you have similar luck!
Again, thanks so much, Bernd!
Brian