In Liferay 6.0 GA4 Community Edition there is an error in the CKEditor configuration; different configuration files are used to define the editing toolbar for the web content and other areas depending on the browsing path. This results in an issue where the toolbar changes seemingly at random. This is fixed in the Enterprise Edition and for future versions, but for those of us using the current Community Edition, the following workaround is useful.
The most problematic disappearing item for my use case is the spell checker; the same method can be used to restore other buttons as necessary. Back up, then apply this
ckconfig.jsp patch to the Liferay root web app. For the tomcat download this is located in the
liferay-portal-6.0.6/tomcat-6.0.29/webapps/ROOT/html/js/editor/ckeditor/
directory. Shut down Liferay, remove the tomcat work directory to clear the cache, then restart Liferay.