Right, the editor expects you to enter a string so you have to put it in quotation marks and you have to escape any quotation marks inside the json string with double quotation marks.
Eg.
{"c2array":true,"size":[30,8,4],"data":[]}
will work when loaded from a file but if you want to paste into an event you have to change it to:
"{""c2array"":true,""size"":[30,8,4],""data"":[]}"
Thanks again, at least I know now how it all works and hope that it can and going to be changed in a future release.