Scrolling issue MFC

Referencing my question @

https://stackoverflow.com/questions/...crolling-issue

Here is the video demonstrating the issue I am having: https://m.youtube.com/watch?v=6RHYADs-TSg

In the original stackoverflow thread that is referenced in the above link, someone said the video looks to be a scrolling issue rather a flickering issue.

Now in the stackoverflow link I supplied, I gave the scrolling functions which seem to be OK.

Does anyone see anything wrong with them or am I missing something or doing something incorrect?

All help is appreciated.