I don't have access to that code right now, so i'll have to look into that tonight.
Best guess though: it happens even without SimpleHTMLEditorField.
Errors are not limited to the SimpleHTMLEditorField, but they also popup in other JS files.
My reason for pointing out SimpleHTMLEditorField is that because of the errors the fields don't work.
Rest of the application seems to work fine, with and without the error.
If i remember correctly the errors did disappear when i disabled DOM and IG and removed any DOM fields in custom code.
This i will also double check tonight.
I'm using the latest trunk versions of the modules.