I am facing a problem which I was also able to reproduce in the linting demo.
If you have a decoration widget in the middle of a text, the cursor goes to a weird position when it gets close to it. This only happens when you place the cursor after the widget and then move it backwards.
Browsers do a lot of weird things like that around non-plain-text nodes. You can try finding a styling kludge to work around it – in this case maybe setting .probarrow's position to absolute works – but unfortunately there’s no general solution that ProseMirror can provide for you.
That helped, thanks!
