This is little annoying bug that I fixed and I thought I'd just share it with everyone in case it happens to you.
If you try to edit the social block at the bottom of the page, and you want to edit “content”, it opens the wysiwyg editor automatically and removes the icons, leaving only the text. So if you save (wether you make changes or not), the icons are gone.
To get them back, you need to click on “source” (I use the CKEditor, I couldn't find “source” on Redactor wysiwyg), and add this line anywhere you want the icon:
Once you save it, it's fixed. But if ever you want to edit it again, you'll have to paste in the icon code.
Here's the original code if you want:
And for Twitter: