CodingForums.com - Assembly Scroll-Down Problem

I am currently developing a game in assembly, and have a serious problem - TASM won't let me draw a pixel on the down-right corner of the window (being 39X24, since i'm using mode 13h\4h). Whenever a pixel is about to be drawn at that spot, the window scrolls down and doesn't draw the pixel anywhere at all.
The problem is not related to the graphic mode I use, as I tried several others with no success. It also have nothing to do with anything included in the game itself, because even when I tried to draw a single pixel there, unrelated to the game, the window still scrolled down.
This is my code for putting the pixel on the screen:

Code:

mov dL, 39

mov dh, 24

xor bx, bx

mov ah, 2

int 10h

mov dl,254

mov ah, 2

int 21h

Does anyone knows what could be wrong?