Shifting to the right

depending on the page, the whole mainWrapper shifts to the right a couple of pixels.

I don't like the header hopping to the right and the to the left from one page to the next.

Has anyone else experience that, and I can't quite put my finger on how to correct that.

v.1.3.8a

Nope. You have to give a link to your site to see whats actually wrong with it. But with the standard installation of v.1.3.8a there is no such problem for me. If there is a problem try to copy all installation files again and see if the problem is still there.

Finally I found the problem.
It's the scroll bar!!!

The scroll bar shoves the whole page to the left and everything pops back to the right when it's not needed.

Can we shut the scroll bar off somehow so it doesn't behave this way ?

You can always show the vertical scroll bar so this does not happen. Not sure if its a good idea to always hide to scroll bar even when its needed.
To always show the scroll bar add

try:

html {overflow: scroll;}

or

html { margin-bottom: 1px; }

See http://snippets.dzone.com/posts/show/217

to your css file.