I've got the same problem but more questions. I first had the problem with d12, I simply decided not to use .d12 and wait for the next version hoping this "feature" would be "improved".
Got .d13 today, with the same problem. In full screen it won't stretch, and leaves everything in the upper-left-hand corner. I tried comparing my previous init.txt to the new one in d13, and the only seemingly applicable difference I could find was [BLACK_SPACE:YES] instead of NO. From what I understand from the comments in init.txt, changing this back to NO should relieve this problem, and give me full screen. It doesn't.
I run my little laptop at 1920x1200 - I can't even use my mousewheel to zoom in that far. I don't want to change my compy's resolution every time I play DF. So what's the deal? Why was BLACK_SPACE's default changed to YES in the newer versions? What the crap does it do? 'Cause it either doesn't do what it claims to do, I'm misunderstanding the claims, or it's simply broken. Anyone know a no-hassle way of fixing this, or should I stick with d11?
And yeah, none of these problems are related to stocks menu scaling... in fact, I never had problems with that. It's just this new version, nothing stretches at all. Nothing.
Thanks. <3
EDIT: The best I've been able to manage, messing with init settings is to get [in full screen] approximately 1/3 of the bottom of my screen as black, with everything fitting fine left-to-right. Everything just looks vertically crammed. Horizontally everything fits the exact same as in previous versions. Prior to .d12 everything would look as properly proportioned text, now it looks as if my text is being crushed. Everything is getting "stretched" vertically, in that it's going the whole 1920 pixels across, it just won't stretch the 1200 up and down anymore. ... anyone know why. What is different now D:
And I'm not using any special graphics tilesets or anything, and haven't in the past. I like my DF looking all roguelike.