Interesting ::)
Which OS version? Console is maximised, I suppose?
Just checked with Win XP, and that looks indeed like what you posted. Unlike Win7 & Win10, the console isn't enlarged enough by the invoke ShowWindow, rv(GetConsoleWindow), SW_MAXIMIZE. You have to enlarge it manually in the console properties, then save "for all future windows with the same name", and restart. Then it works.
On Win7, the display refreshes immediately, i.e. in milliseconds. With Win10, it seemed initially very slow, but now it has become fast. I have yet to find out if there is a pattern - mysteries of Windows 8)