Seem to be having a weird issue with StructuredDiscussions, the editing window that shows up under the Topic name doesn't want to allow me to enter text UNLESS I have the Debug line added (?Debug=true), with that line added it works with no issue. I confirmed it works with both Source and Visual Editing so it doesn't seem to be a Parsoid issue. Below are screenshots of what I'm referring to:
Topic on Extension talk:StructuredDiscussions
Open the developer tools of your browser (hit F12) and look at the console for any JavaScript error (they usually appear in red color). Maybe there's some error causing this.