When combo box doesn't have a value it's hard to see if interaction is possible

[nephros]

Are you using the Keyboard settings simply as an example (i.e. your complaint is about ComboBox in general), or is your bug actually about the Keyboard settings behaving in this way (i.e. you want a different display in that dialog when there’s an invalid value in the dconf key)?

EDIT: Ah it seems to be the former, as you have also done Keyboard not falling back to default layout when it can't find active one.

So about ComboBox:

The docs say:

Notice the value property defaults to the text of the currently selected option. In the above example, the current selection defaults to the first item in the menu because neither currentIndex nor currentItem have been set.

So if there is nothing displayed in the case it’s uninitialized, that seems to be a bug on the application side…
That being said, the behaviour of ComboBox has always been a bit fragile, an overhaul would be beneficial in any case.