Computed optionsCaption not disappearing fully in latest build

With 2.2.1, if `optionsCaption` on a select element was set to the value of a ko.computed that only returned a string if the observable used for `value` was defined, the caption would not only disappear once the first item was selected, but there wouldn't be a space reserved for it in the dropdown list anymore. This is what I would expect and want to happen, as seen [here](http://jsfiddle.net/neverfox/gJ9hN/). Switching to the latest build (2.3.0pre, SHA db6eae5), it no longer works this way. There is now a blank item in the dropdown list where the caption used to be. [Here](http://jsfiddle.net/neverfox/PxDDG/) is the same example using the latest build.