Visual Composer won't accept shortcode…

First off, fabulous plugin. It does precisely what I need.

I’m running into a small problem though with Visual Composer. I want to set it up as a VC Element to make it easier for the client to insert the button on-page, but VC is saying “Please enter valid shortcode to parse!”. I know the shortcode works, embedding onto the page manually displays the icon just fine, it’s just for some reason VC isn’t registering it as a valid shortcode?

Anyone else come across this problem?

https://ww.wp.xz.cn/plugins/print-o-matic/