SAPGUI HTML- - scrolling on search output is slow but result (ALV) is very fast

I am not sure why this is the case.

when I click on F4 on customer field and get the results back , scrolling thorough the output is very slow( scroll 20 lines but doesn't change until I stop scrolling , then 1~2 seconds later the changes are reflected. (Screen shot 1)

But when I am on the output screen, scrolling is pretty fast (ALV)even with large amount of data.( Text output is extremely slow too)