To reproduce, on vBulletin Connect 5.5.5 create a new post with a hyperlinked image as source:


Code:
URL="https://vbulletin.com"]IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/www.vbulletin.com\/magento\/skin\/frontend\/vbulletin\/default\/images\/logo.gif"}/IMG2]URL]
...