Image lightbox is still displayed for silk icons, added from image plugin

Steps to reproduce

1. Enable lightbox from Administration -> Look&Feel -> Lightbox
2. Go to a page and insert an icon using the Image toolbar menu, then select Icon tab and type "car" and select icon
3. Save the page and hover the car icon

Expected result: the image toolbar is not displayed

Actual result: the image toolbar is displayed and the lightbox contains all the icons inside the page content