When I use the Draw.io extension, VisualEditor shows the html tags insead of an image in edit mode.
The same problem exist with extension PageForms, the edit with form link becomes <a href=...
Topic on VisualEditor/Feedback
ok, found the answer: this is a parsoid (security) limitation. Added the 'A' and 'IMG' Tags to TagWhiteList in WikitextConstants.js and now it works