Problems with my Sprite & Overlapping Background

[AMSDOS]

At the moment I'm trying to get my Viking with Background screen to move down the screen without destroying the background, though when I hit the down arrow key ("↓") my viking does some sort of jump (possibly because the grab routine isn't quite doing what I need it to), and if I press the other arrow keys it's like my viking has moved to the bottom of the screen without being shown as moving to the bottom.


I've had to modify the Grab Routine (which was Sean Mcmanus' routine from ESD2), to have assembly instructions interact with it instead of BASIC, the original routine was also using the Firmware (&BC1D) to return the screen address, though I'm trying to use findcolumn routine to produce a screen address and from that grab and capture that portion of background screen. Personally I thought it would of worked though I'm missing something or doing something wrong.