Strike-through doesn't work well with todo lists

[f1ames]

Creating strikethrough text for the existing todo list item looks correct in the editor:

However after saving it is changed to:

And the markdown for it looks like this:

You can add [ ] manually in the Markdown editor, but then when switching to RTE it is lost again (the message about unsupported markup is shown 👍), which means in such situations you are stuck with the Markdown editor.

[Reinmar]

That's upstream. ckeditor/ckeditor5#5779

Unfortunately, the entire model<->view mapping in this feature requires a rewrite. The feature is buggy as hell at the moment and there's little option that we'll have a chance to fix it anytime soon.

[mateuszzagorski]

Closing, as it does not seem to be replicable anymore after the upstream fix.