Just got DFHack to check, and it looks like that tries to do something (I get a block of random characters below the game screen outside of what would normally be drawn), but it doesn't affect the actual game. It seems like the output in TEXT mode might not actually check what size its window is and just renders at the default 80x25.
Are they just garbage characters, or what are they? How much sense do they make?
I believe that there is probably another thing somewhere in the render engine which would change the assumed resolution. I'd do some tests, but I don't think my VM is suitable enough to run DF.
I might need to go and disassemble the Linux version to see how it figures out the grid size to use (grid being 80x25 at default), and where it stores it for the render engine. In fact, I could probably work on the Windows version, since (in theory) the render engine just gets switch/case selected (or something like that), and the actual dimensions for the drawing handler (one step closer to high-level code than the render engine, which is e.g. "2D" or "TEXT") should be managed the same way between the two versions.
My experiment in Windows, at the title screen, widening to 81x25, caused some stuff to be cut off the right edge of the window (e.g. the version number was "v0.40.2"). But it is indeed possible that the interaction between the draw and render engines is more complicated than I thought.
+1 for official support for changing this.
also +1 for adding the functionality into Windows, since one could easily use xterm or mintty to get support for Unicode and all the keystrokes...