Thanks for trying it out! Always glad to hear people are looking forward to it.
The file writing problem is almost certainly from how I try to make a folder in Documents\My Games\ to put the settings in, and I wasn't checking if the My Games folder even existed, it should hopefully be fixed in the next demo.
Is the Z-fighting only when you're hovering over it for interaction? Because I draw the highlight as another pass so that's a very likely place for it to happen. This is inconsistent on different video cards so I might try a different technique.
I love how people appreciate the "feel" of the game, it's been a big sticking point for me (and one reason for why I don't use an engine) so I'm very happy that the effort isn't being wasted.
I can't guarantee the next demo will be any sooner, we'll see how I much work I can get done on the editor tools, but I'll be looking forward to hear from everybody again then!