Hm. Well, it could be one of two things, and after some digging, I found that it could also be an oversight on my part. ;-)
The buttons are hooked into a filter called 'the_excerpt', which is similar to 'the_content'. Almost all developers know about 'the_content' filter, but very few know about 'the_excerpt'. This is fine when a developer uses the built-in WordPress functions, like
the_excerpt(), which filters the text automatically. But when they access the text directly, they can sometimes forget to run the filters on it.
So, one possibility is that they're accessing the excerpt text directly from
$post->post_excerpt and forgot to apply the filters.
After some digging, I found that the WordPress built-in function
get_the_excerpt() runs a 'get_the_excerpt' filter, and not 'the_excerpt'. And of course, to make things all standard, a 'get_the_content' filter does NOT exist. :-p
So, to recap, if your theme uses
$post->post_excerpt, your template(s) will have to be updated to use
apply_filters('the_excerpt') on it.
I have to look into hooking into 'get_the_excerpt()', which is tricky because text can get filtered twice that way. Give me an hour and I should have a new version of the plugin for you to test.