Connected drop down shows initial value even when show initial text is set to None

I have two drop downs City and Specialty. Specialty is connected to dataset and City manually entered drop down items. Specialty dataset is filtered by the city dropdown value. So its like user first select the city and in specialty drop down only specialty visible which are available in that city.
For both show initial text is set to None. Below is how the drop down looks at initial page load.

Now when I select any city it will automatically show one available specialty in the specialty drop down. In below example I have selected the city Bhilai and Specialty drop down automatically shows the ENT. I want specialty to show only when user selects from drop down other wise it should blank