See attached example. This was generated by printing 10 lines using mvwaddstr() and then some single characters at different positions using mvwaddch(). A character displayed with mvwaddch(w, x, y, c) will overlap character at (x+1, y) by 1 pixel.
You don't say what platform this is. Unless it's SDL or X11, I'd say it was an issue with your terminal.
Platform: Win32 console
The problem occurs when using the following code:
mvwaddnwstr(td->win, y, x, buf, n);
Any value for 'color' that is nonzero (white color) gives the glitch.
I've recompiled ncurses for Windows and tested both ncurses and pdcurses with the following code:
mvwaddch(win, y, x+1, somechar);
mvwaddch(win, y, x, someotherchar);
With ncurses, no problem.
With pdcurses, the previous code 'eats' the first pixel to the left of the character at (y, x+1).