I found and reported a severe bug in the VisualEditor, where it unexpectedly deletes without notice all template transclusions whose parameters list contains some HTML comment (e.g. some infoboxes at top of pages, when they contain lots of parameters, or some comments intended for editors explaining some values or its expected format). The deletion is not visible while saving and reviwing the page, but applied when the save operation is confirmed.
On some pages, this is highly destructive. No reponse for now. This is a bug in its own parser.
The Visual editor should have a checbox option to show (and edit) the HTML comments in the page preview, as if it was a content tag.
The same is true when parser functions are included (but less critical, because parser functions are usally within templates, and templates are made by editors using the wiki code editor for now (the VisualEditor is still not usable for templates, it lacks some important thingsn notably the capability of ediring them in a property sheet where you can view and select or add/delete the parameter to edit, and where its edited content should also be made in tge previw pane, and multiple preview/property sheets that are recursively included should be switchable using some ordered navigation tabs at top of the editing window).
There are still sever issues as well when saving pages : categories can be moved anywhere on the page.
Finally, whitespaces are also trimmed everywhere in the page (sometimes incorrectly as well, breaking the existing code), even in paragraphs we do not edit. It complicates things a lot when viewing diffs. And it makes the editing of the modified wiki code much more complex (when indentation is lost, e.g. when working with reference templates).