Steps to Reproduce

Run fiddle
http://zkfiddle.org/sample/gg8g6o/3-radiogroup-callback-bugs

2 actions to test:
1- during doAfterCompose, "s1" is set as selected
2 - add s3 to model (click on 2nd button)

Current Result

1- radio set as selected in model before rendering is not selected
press 1st button (select s1) to add to selection after rendering
2- adding entry to model causes NPE

Expected Result

1- radiogroup should follow model selection
2- radiogroup should be able to add entries to model

Debug Info

both caused by the AFTER_CHILD_ADDED event from
https://github.com/zkoss/zk/commit/5b4e2af427ff9cc5c640f8faf47767c0668f6939#diff-46516529e62220b1c4c4efe660aa50d4R309

in case 1:
the after_child_added event triggers org.zkoss.zul.Radiogroup.fixOnAdd(Radio) after setting the selection from model.
fixOnAdd set the selection to false in this case.

in case 2:
the event listener is added to parent radiogroup and is never removed. It will trigger when any child is added to the radiogroup. If the child doesn't have a _group value yet, this will trigger a NPE

Root Cause

Workaround

replace org.zkoss.zul.Radio.onPageAttached(Page, Page) to removed the async. (class attached for 8.5.1.2, note: may cause radiogroups to not recognise nested radio components if not direct child)