I can not, for example, hide a button (spelling for example) using CKeditor settings:
If I hide it, I can see how it's hiding at the moment at the "live preview toolbar", but when saving changes, I get it active again when settings page is refreshed.
My crm-ckeditor-default.js or crm-ckeditor-civimail.js file (depending on the tab I'm changing the setting) has the file modified date updated, but without changes there when I was hiding a button on UI, but, and that's for me a headache, I can see changes saved when I'm adding/supressing a plugin, for example:
config.extraPlugins = "colorbutton,justify";
About plugins settings, another unexpected behavior: when at demo civicrm site, using the same version (latest, 5.10.3) you add a plugging, for example "justify", you get, at the moment, some buttons added at live preview toolbar. But not for me: I haven't got any changes.
Ps at civicrm demo site I have not got this issue.