[dartho]

@Fungsten - I've looked at the code which adds the useragent string, it only gets applied if teh following is true:
if (($styleid==$vbulletin->options['mo37_mobile_style']) && ($vbulletin->options['mo37_post_text'] != ''))

ie. if the style the user is currently viewing your site with equals the style you have selected as your mobile style in admincp AND you have configured text to display (ie. Posted via Mobile Device) THEN append the 'Posted via Mobile device' message.

I can't see how this would be happening unless the user is viewing your site via the mobile style.

Could you check this with the user? A screen dump and their useragent string would help.