Incorrect mouse selection in QTreeView with ExtendedSelection and stretchLastSection == false

If a content of a tree view doesn't occupy the whole viewport area (e.g. when stretchLastSection == false), then mouse selection that goes outside of the content produces incorrect results:

1) if the selection is started outside of the content, then all items from the top of the selection to the bottom of the content become selected

2) if the selection is started inside of the content, then it stops changing when the mouse goes outside of the content