Ricky
in my experience, this is likely related to poorly formed XHTML in one or more formatted text fields. When you resized the font, the text was reformatted with proper XHTML. For troubleshooting purposes, I have put a text box control on the web page(s) where there are CKEditors, displaying the same attribute as the CKEditor does. This will help you to see the issue, usually. It may be something like an unterminated break tag. Use of the XSSSanitize Java Action from Community Commons has reduced the issue, but not eliminated it altogether. Most often, I experience this issue when formatted text is copied and pasted directly into the control, without using the Paste from Word feature of CKEditor.
Not sure if that helps or not.
Mike
P.S. see here for a relevant recent post in the forum - you're not the only one experiencing this kind of issue