Free: I'm not sure. It'll be a long, long time til I make that call either way. Certainly not forever, but the final game looks to be 10+ hours and I'll probably start charging a marginal amount as "Early Access, get the full game at no extra cost when it releases" at some point when the content exceeds several hours. The demo will always stay free once it hits a point I'm satisfied with.
Black rectangle: Bug, and not one I've heard of or seen. The title text is made up of 23 images anyway so I can't imagine how that'd happen. Could you send me a picture? To Discord at jakefriend #4098 or email at jakefriend.dev@gmail.com, thank you!