In general, the DropDownList widget is designed to detect whether it is loaded in a mobile device. If touch actions are available, we won't focus the input element on click to open the popup element. This is done to prevent clashes with the virtual keyboard of the device. This approach is tested and works with iOS, Android (latest), Windows Phone OS (latest).
Could you give more details about the device you are using? Could you also test the widget on our online demos too:
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