Form data within a gadget are not saved.

I was able to reproduce on 16.10.13. It seems something changed in the way dashboard gadgets are rendered. The gadgets end-up being rendered twice, and the WYSIWYG editor doesn't like the fact that two instances are created with the same name (one hidden). You don't notice the problem if you set your preferred editor on your user profile to be Wiki, rather than WYSIWYG, because even if there are two text areas generated with the same name, one hidden, the value from the first one wins when you save the dashboard.