Symptoms

Control will render weirdly when you have only one option in the Choice list and dont specify a Display value
 

Diagnoses

This is introduced behavioral change. It affects all controls that makes use of Static List Items as a data source namely Checkbox List, Radiobutton List, Dropdown List, Choice control, Multiselect control, and Listbox control.

The behavior is only encountered when a single item is specified with no display value. Specifying two or more items, each with no display value, will not yield the same result. Using a space as a display value will also not help, the resulting string is trimmed, causing the same issue.

It has a failing runtime effect on the checkbox list, radio button list and dropdown list controls as the values string passed at runtime is empty and cannot be parsed as XML
 

Resolution

Logged as a bug to be fixed in the next release
As a workaround pass a display value for the control.