Generally speaking, the main purpose of the Kendo UI ComboBox is to allow custom values
along with selection from a predefined list. When typed text is not part of the datasource, then it is considered as custom
and both text and value are synced. This is the main difference (to be honest, it is the only one) between combobox and dropdownlist.
If you would like to prevent custom values, then the best solution is to use DropDownList. If using a dropdownlist is not possible, then please refer to this how-to demo
that demonstrates how to clear the entered custom value.
To sum up, the described behavior is expected and intended. If this is not desired, then the best solution will be to use DropDownList.
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