Header Alignment Problem

Recently I noticed that the images in my header are misbehaving.

I am using the header layout with the masthead and logo at the top od the page, where the logo is located in the center of the masthead. The masthead has an image on the left and right with a space in the center for the logo to appear.

Until lately, the header behaved properly, but now the masthead image on the left is partially covered by the logo. It appears as though the horizontal dimensions for the masthead, and or the logo have changed, but not by me.

The only changes I have made that might be associated with this phenomenon is that I updated to WordPress v2.8 and installed MS Internet Explorer 8.0.

Can anyone help with a fix.