This add-on doesn't affect the normal share function for threads at all, so it's a setting or change somewhere which is globally affecting all share links, not just this add-on.
This is the code I use to pass the URL to the share template:
Code:
<xen:set var="$url">{xen:link 'canonical:threads', {xen:string censor, $featuredThread}}</xen:set>
This is the code XF uses:
Code:
<xen:set var="$url">{xen:link 'canonical:threads', $thread}</xen:set>
As you can see, both bits of code are the same as far as the canonical link is concerned.
Which other add-ons do you have installed?
Have you manipulated the routes in any way?