In filter mode, QFutureInterface<int>::addResult(const T *, int index) reports total rubbish.
Consider this sequence

QFutureInterface<int> iface;
iface.setFilterMode(true);//sic!
...
iface.reportResult(&value, 0);
iface.reportResult(&value, 1);
iface.reportResult(&value, 2);
iface.reportResult(&value, 3);

would trigger (in an attached QFutureWatcher) resultsReadyAt(begin, end)
with ranges:

0, 1
1, 3
2, 5
3, 7

Which makes zero sense. The bug is that the end of the range when reporting ready results is too large.