According to several sources (which will be posted at bottom of this post), Hotmail breaks special characters and turns them into graphical emoji since recently.
Here’s an example of the (r) special character being turned into a large image in Windows Love Hotmail’s own email:
Thankfully, Elliot Ross from Emaildesignreview.com posted a workaround solution to this a few days ago here.
More info on other email marketing blogs can be found here:
Campaign Monitor: Hats off to hotmail for replacing symbols with oversized emoji
Retailemailblog: Alert: Hotmail converting some symbol characters into images
Responsys: Hotmail Replaces Copyright, Trademark and Registration Characters with Images
Yesmail: Quick Fixes to Hotmail’s Symbol Rendering Issues