So, I am not sure why it is having an issue, and I don't like messing with the source code, but to get the ExtJS htmleditor to show up, I have to comment out a few lines of code in the assets/components/mxcalendars/js/mgr/widgets/mxcalendars.grid.js:
Lines 581 and 605, I have to hard code it to
and comment out the check statement.
then, I have to comment out the tinymce var check at line 824.
I use ckEditor (soon to implement redactor) on the site.
And even when I installed TinyMCE to try to get things to work (even set which_editor to TinyMCE to see), the RTE would not show up.