XHTML disrupted by Mobile access

Screen shot of the XML error, lots of code.I'm not sure whether to put this down to an issue with my (mobile) ISP, or whether it should count against using XHTML sent as application/xhtml+xml? I've recently found that even a well authored site using valid XHTML can display as an XML error in browsers that support XML mime types.

The site was using Internet Explorer's conditional comments to overcome some limitations in IE, and a reverse conditional comment for non IE browsers:

<!--[if !IE]> <-->                                                                                  
        <script type="text/javascript" src="scripts.js"></script>                            
<!--> <![endif]-->

Unfortunately, when sent over my mobile connection (Orange) the page is reformatted, even though I'm only using it as a modem. The file is stripped of line breaks, and that comment comes out as:

<!--[if !IE]><-->
  <script type="text/javascript" src="/scripts/basic.js"></script> 
<![endif]>

Missing the close of the comment, the strict display mode triggered by the mime type means that only an XML style error message is displayed.

I guess this has to be added to the list of issues (such as user-added content) that makes an XML mime type difficult to manage?