Page shift

[mvlcek]

I've seen this on pages created with other tools and it drives me up a wall. In the end, it will likely be something trivial, but in the meantime, I'm stumped. Here's what happens:

Create a series of pages, two will work
Using either the menu or browser navigation click back and forth between pages.
The left edges do not remain aligned. There is a noticeable shift.

Thinking it was an illusion, I covered the display with a straight edge, but there is an actual misalignment between the pages. Thinking it was a template-specific issue, I changed themes, but the several I tried all did the same.

Ideas?

Maybe you have short and long (with scroll bar) pages.
If you have a scrollbar, a centered content will be slightly more to the left, as there is less browser client area.
You can always turn on scroll bars with CSS overflow-y: scroll.