Thread:Extension talk:WYSIWYG/How to strip unwanted styles ?/reply

I am not expert on this field but I would guess that this issue is related to version of CKeditor (upgraded from 3.6 to 4.3.4), new version may work differently than the previous one.

Have you tried config.extraAllowedContent instead of config.allowedContent?

You can find more information here:
 * CKeditor 4 advanced_content_filter
 * CKeditor 4 allowed_content_rules
 * CKeditor 4 disallowed_content

In latest CKeditor 4.4.0 version, there is also a new setting "config.disallowedContent" available. For this reason I have upgraded CKeditor to version 4.4.0 in #6 bundle (with version >=05.05.2014).

In the end of page disallowed_content there is an example about "How to Allow Everything Except...", perhaps you can use that approach to solve this issue.