ShiftModifier is ignored when simulating mouse clicks

Qt::ShiftModifier is ignored when using sendEvent() or postEvent() to simulate mouse clicks on item views - an extended selection is expected but only the last-clicked element is selected (probably because current selection start index gets overwritten).The example app TestApp_selectMultipleRows.zip shows the regression: it works as expected with Qt 6.5.0 but fails with Qt 6.5.8 and 6.8.0.

The issue doesn't occur when:

• clicking on items by hand
• using QPA
• using Qt::ControlModifier

Initial analysis

This regression affects replaying recorded interactions in Squish: SQUISH-18502 - see analysis details in comment section.
Our investigation suggests that the issue started after the following fix: QTBUG-127381.