Yes, spot on @Andy_Vaughan, this has been noted in our team so that we can review feeedback.
The reason for this is to make it clearer which elements have overrides, and which elements contain static content. If an element does not have an override bound to it, one can assume that a designer wouldn’t want to allow the element to be edited.
It would likely be confusing for a content editor to edit some text on their site, and see that it updates everywhere (static element) and then update some other text (overriden content) and it only changes that one instance.
We’re happy to hear to feedback on this, as of course we’re still in the BETA phase of symbol overrides.
To confirm, even if an element had the “Collaborators can edit this element” checked, once it’s converted or added to a symbol, then it’s unchecked.