This topic has been discussed on TG and I'm sure there are some good reasons as to why this happens.
To be honest, a web site visitor is not interested in any technical or browser problems, as to why this happens.
All that is seen, is something that looks unprofessional.
Click here to see the jumping problem.
You will see that when you use the menus along the top and you go from page to page, things jump right and then left, when the page appears to get centred.
Many other sites, jump from left to right.
I'm sure, Xara boffins, can find an answer because many sites do not jump.