Back / Forward buttons on mouse also cause keyboard event for the same event always

When clicking back / forward buttons on mouse (fex MS IntelliMouse Explorer 3), keyboard event for the same back / forward is always received too. This effectively leads to double back / forward events. If mouse is hovering the Window title when back / forward is pressed, mouse button click event for the back / forward is not received at all, but keyboard event is still received.

Steps to reproduce:

• Run attached sample
• Click back and forward buttons on mouse (or tilting the wheel on mouses that support it)
• Click back and forward buttons while mouse is hovering title bar
• Observe the log output
• EXPECTED: Only one back / forward event is received
• ACTUAL: Double event is received, one for mouse click and one for keyboard press, on title bar only keyboard press is received

Qt documentation states that some mouse drivers cause keyboard press event to be sent instead of mouse click for the extended buttons, but does not state that double event is sent.