Listbox allows selection with checkable="false"

Steps to Reproduce : Case 1

Demo here:
http://zkfiddle.org/sample/3c3tr14/1-listbox-selectall-checkable-false

By ticking the checkbox in the listbox header, all list items are selected, even those with checkable="false".

Steps to Reproduce : Case 2

1. run listbox-checkmark.zul
2. click listhead to select all
3. scroll down to last item

Actual Result

Some items without checkmark are selected.

Expected

only items with checkmark are selected.

Debug Information

Those items are not fully rendered because of CE ROD, so their isCheckable() returns true before we scroll to render them.