jquery - Changing class during scroll jumps to the top -

I am trying to make alerts an alert so that

1. the alert is immediately below the header When the header is visible on the screen
2. Alerts at the top of the screen are at the top of the screen.

When I do this (I've tried jquery and twitter bootstrap), and I drag the scrollbar down, the scrollbar jumps to the top when the CSS class changes on the element.

I am running in Chrome, V38.0.2125.104

Run this with a width of 750px or less to see this problem:

It has been found that adding / removing horizontal scrollbars was causing the jump on top of the page.

I was able to make the horizontal scrollbar consistent by adding overflow: none CSS