You could change this on your wiki by modifying the shortcut definition :

Currently this is:

    
    [shortcut name=debbug url="http://bugs.debian.org/%s" desc="bug #%s"]
    

You just have to use:

    
    [shortcut name=debbug url="http://bugs.debian.org/%s" desc="#%s"]
    
(do use double bracket here, I do not understand why the shortcuts [[ikiwiki/PreprocessorDirective]] are parsed inside the code block).