QList::insert(): Index out of range

Oddly a simple example with Qt5.12.5 32bit works good but with Qt5.15 -32 bit prints QList::insert(): Index out of range and this does not crash.
Attached is the example.
This prints it when series->append(set0); is called.

See "Deprecate calling QList::insert/removeAt with out of bounds index" ebf695bc779a63a5730df05ab246305c0ab342e4 https://codereview.qt-project.org/c/qt/qtbase/+/276371