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"]

(I use single bracket here beacause of wiki links still processed inside code blocks)