Found another corner-case bug: If you create a Multiline field and flag it Sensitive, when editing an item with this field, the content of this field is not obscured.
To be more clear...
When viewing an item containing a sensitive multiline field, you do see the •••••• instead of the content.
But when editing such an item, the sensitive multiline field is fully visible (and there's no eyeball button to show/hide the content), even though other sensitive fields work correctly.