With your application maximized, but still in a window, you're using a non-standard resolution. (not 800x600, 1024x768, etc..)
DirectX / DBPro is doing it's best to "fit" your text into that, but it will chop rows of pixels (in 2D where text lives) to make it work.
Set your display mode to a standard resolution that's smaller than your desktop (800x600 for example) and then maximize that. You'll see what I mean. It stretches the text to make it fit the area.
What you are doing by setting the display mode to close to the desktop resolution is you are losing lines in your text as it tries to compress it to make it fit in the maximized window.
Try
set display mode Desktop width()-48, Desktop height()-64, 32
and then maximize the window and see if the problem doesn't go away.