New Post: {cke_protected} being added in view mode for any span that has a class

This seems to be a recent issue, and not sure what is causing it. If in source mode I have this HTML:

<h1 style="text-align: center;">TEST TITLE</h1>

<p>
<span class="textLarge">THIS IS INVISIBLE IN WYSIWYG MODE</span>
</p>

then when I switch to WYSWYG mode, the content in the span is invisible, and when looking at the page source the editor is being filled with:

<!--{cke_protected}%3Cspan%20class%3D%22textLarge%22%3ETHIS-->  

etc etc

so the user can never edit the content, unless if they went into source mode and removed the class="textLarge" from the span tag and went back to the WYSIWYG mode, the content appears exactly as it should.

Any idea what may be causing this?