[bug] radios group > selected value > all values like first value

Hi there,

possible bug in field "radios group":
When i add behavior "selected value(s)", all values become first the first value/options

[example 1]
options:
y=yes
n=no
behavior: none
=> success

[example 2]
options:
y=yes
n=no
behavior: Selected Value(s): n
=> error; the forms shows "(•) yes" twice; html source as follows

[example 2 html source]
<div class=" fields ">
<div class="field">
<div class="nui checkbox radio">
<input type="radio" name="bShowContributor05" tabindex="0" class="hidden" value="y">
<label>ja</label>
</div>
</div>
<div class="field">
<div class="nui checkbox radio">
<input type="radio" name="bShowContributor05" tabindex="0" class="hidden" value="y">
<label>ja</label>
</div>
</div>
</div>

How can we turn this effect off?
Thanks!