I couldn't replicate this issue. Does it only occur for sites upgraded from J3.5 to 3.6? Tested with a fresh install of J3.6 alpha 2 with the latest version of com_patchtester, and PHP 7.1 and PHP 7.0.
@JoshuaLewis the issue appears after upgrading to 3.7.0 (beta 1), it is related to changes (new features) in the TinyMCE plugin in upcoming 3.7.0 version. Please test after upgrade to 3.7.0 beta 1.
I have tested this item✅ successfully on df4fb73
This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/13901.