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Yes you are correct.

Here is the explanation why and workaround (taken from java-doc of ButtonGroup):

"Initially, all buttons in the group are unselected. Once any button is selected, one button is always selected in the group. There is no way to turn a button programmatically to "off", in order to clear the button group. To give the appearance of "none selected", add an invisible radio button to the group and then programmatically select that button to turn off all the displayed radio buttons. For example, a normal button with the label "none" could be wired to select the invisible radio button."

Defining explicitly selected to false did not change the inheritance behaviour.

this is basic behavior for the object's properties:
if you want some property to have some specific value, you have to set it explicitly.

In case of checkboxes, 'selected' has default value false. That is why first time (in 1st iteration) it appears unselected, but on the next iteration it will not reset its value to default, so it will be selected or unselected (depends on the actions)

Just explicitly set 'selected' to false for the 1st iteration and it will be working like you wish.