"Error: Cannot assign to read-only property" in delegate

[wspilot]

Hi,
Qt 4.8/Sailfish-Ubuntu
I have two Listviews in QML.
Both are set via C++ ():
@rootContext()->setContextProperty("myCheckListHeadings", QVariant::fromValue(clHandling->checkListHeadings) );//data
rootContext()->setContextProperty("myCheckListItems", QVariant::fromValue(clHandling->checkItems) );//data
checkListHeadings.append(new CheckListItem(chked, clName));
checkItems.append(new CheckListItem(chked1, line));
@
chked, clName and chked1, line are valid bool(false)/QString values
etc.
Both listviews are filled with the data from C++.
Both listviews have delegates with:
(MouseArea) Onclicked:
@checked is true
@

In the first list checked is indeed set to true,
the second list generates error:
@
Error: Cannot assign to read-only property "checked"
@

I have seen bug reports on this issue, but it is unclear if it was solved.
Also strange that one list is working OK, and the other fails.
Any hints?
Thanks.