Ok, I have some evidence of something not working properly.
/assets/components/mxcalendars/js/mgr/widgets/mxcalendars.grid.js: lines 581 and 604
xtype: mxcCore.config.event_desc_type == 'htmleditor' ? 'textarea' : mxcCore.config.event_desc_type
I checked the value of `mxcCore.config.event_desc_type`, and it only returned "h", not the options required.
I checked the MODx system settings - it was selected as "htmleditor". I changed this to "textarea", but the value of `mxcCore.config.event_desc_type` didn't change from "h".
Coincidentally, this value truncation seems to be happening for `mxcCore.config.category_required` also; The value I think should be "true", however it's coming through to the grid as "t".
(Images are screen grabs from Developer Tools)