If a QList contains unique pointers, they get deleted after a new item has been appended to the list.

I.e.
typedef std::unique_ptr<X> XPtr;
QList<XPtr> x;
...
x.push_back(new XPtr()); <-- here all the items of x will be destroyed!

This is a huge regression as it silently breaks compatibility with older code and violates ideology of list-based containers.