[wayfarer]

OK, I have a couple of clues... I think this is linked to a section of button.tpl:

{* $Id: button.tpl,v 1.25.2.2 2006/06/16 10:47:41 max Exp $ *}
{if $config.Adaptives.platform eq 'MacPPC' && $config.Adaptives.browser eq 'NN'}
  {assign var="js_to_href" value="Y"}
{/if}
{if $type eq 'input'}
  {assign var="img_type" value='input class="InputNoBorder" type="image"'}
{else}
  {assign var="img_type" value='img'}
{/if}
{assign var="js_link" value=$href|regex_replace:"/^\s*javascript\s*:/Si":""}
{if $js_link eq $href}
  {assign var="js_link" value="javascript: self.location='"|cat:$href|amp|cat:"';"}
{else}
  {assign var="js_link" value=$href}
  {if $js_to_href ne 'Y'}
    {assign var="onclick" value=$href}
    {assign var="href" value="javascript: void(0);"}
  {/if}
{/if}

I can comment out this...

{if $js_to_href ne 'Y'}
    {assign var="onclick" value=$href}
    {assign var="href" value="javascript: void(0);"}
  {/if}

And the functionality now works in IE. But I'm not sure if there are any implications of doing this that may affect the original reason it's in the code...

Also, with the above commented out, when I mouseover the link, instead of javascript: void(0); I now get this in the status bar:

javascript: document.orderform_16194_1220758753.submit();

whereas normally an add to cart link would not show anything in the status bar...

Can anyone shed some light?