Logo Image disappears in IE

Greetings BFA community!

We are using Atahualpa with a rather non typical layout, placing both the logo and header images on the same horizontal plane. You can see it here:

http://acmac.net/acu/pro/

The positioning was achieved by editing the values in the Atahualpa settings within the WP control panel, like so:

Style & Edit HEADER AREA - Logo Image: Styling

float: left;
margin: 0px 0px -110px 0px;

Header Image - Header Image: Alignment

top right

We were very happy with the result until we tried viewing it in IE v 8 and 9 Beta, where the logo image disappears. Works fine in Chrome, Firefox and Safari.

Is there a custom tag we could add to any of the Ata configuration files to make IE display it, please?

Any advice is greatly appreciated!

Many thanks,

Slava
ACMAC