Column page scroll uneven after auto-update

Hi

I have a site using Hueman theme, which has 3 columns – the main content in the middle and two sidebars.

There has been a recent update which means that when I scroll down the page, instead of the whole page scrolling down, only the centre content moves, with the sidebars staying the same. When you reach a point, the sidebars then scroll down with the centre column, and that point seems to depend on the length of the page/sidebars.

Before a recent update, if you scrolled down the page, the whole page, centre and sidebars scrolled down uniformly. I would very much like to return my site to that state.

Can anyone help?

The site in question is http://www.whisperingstories.com

Thanks in advance