Icon font, underscores in ligatures

At the company I work at, we use an icon font to supply assets to our website to display icons. I set up the font using the icomoon.app application and each icon got it's own ligature, so it would be easy for devs to implement them.

Now I was doing some testing, because I saw that one icon was showing up on multiple ligatures. As it turns out you can apparently_add_as_many_text_with_underscores_as_you_like ?!?

As you can see I used fontforge to check the ligature in the font, and in the html I just put random text behind the ligature, and still the icon shows.

Now this does not make sense for me, you would assume that adding _some_text to a ligature would result in a unique ligature for that particular icon. But apparently _stuff_with_an_underscore don't matter?"

Does any of you have an idea why this is happening?