Layout (theme) problem

I have a very strange problem.

On this moment i working on the browny wind theme.
I will let it scale to the users screen resolution.
And that works (so far so good :P)

But now the problem:
When i hit Ctrl - F5 (see the attachment) the layout is very strange.
When i hit F5 or Ctrl - R (see the attachment) the layout is ok!

It is only when i hit Ctrl - F5.

The problem is in FF and Safari.
In IE there are no problems.

The site is: http://mydigitalworld.nl

I hope anyone knows what the problem is

Greets Kees.

checkRes detects the user resolution.
After that the right .css will load.
But now i have coded it so that always the same .css load.
But i have the same problem.

checkRes is not the problem in that case i think :P

I have found the problem:

.g-thumbnail {
margin-top: 3px;
margin-bottom: 3px;
width: auto;
height: auto;
max-height: 110px;
}

When i delete the width: auto; and height: auto; the problem is fixed.
But in that case the scale is not correctly (see attachment).

Any ideas?