I am attaching 2 pictures to show what's happening in version 2017.2.621.  In the newer release I have to set the font & size specifically or the text is larger that the box.  It was not this way on previous releases.
Here is the code  I am using to get it to display properly.  However, it did work (as in picture 1) with out the specific font items before.

<telerik:RadComboBox ID="RCB1" runat="server" DataSourceID="SqlDataState" DataTextField="abbreviation" DataValueField="abbreviation" Height="200"  MarkFirstMatch="true" Skin="Office2010Blue" Font-Names="Open Sans" Font-Size=".73em" ForeColor="#64758F" onFocus="this.select()"  Width="150px" EmptyMessage="Choose State...">
</telerik:RadComboBox>