grrr, that was it, thanks!
In my actual code, about half of my entry textvariables are using references and half aren't (because I was cutting-and-pasting chunks basically). Of course, the ones I was just now testing were NOT references and the ones that are references aren't in something I expect to update, so I wasn't seeing anything update.
I then just grabbed the chunk of code without the references and tried it stand-alone and didn't see/think to make the textvariables point to references so I assumed I was doing something really dumb..... Which I was :)