Clicking the middle or right button of a Wacom pen generate many mixed middle and right press and release events.

Attached minimalistic example produces following output for Qt 5.6 (expected behavior):

Left click:
press left
release left

Right click:
press right
release right

Middle click:
press mid
release mid

For Qt 5.7, the same application produces:

Left click:
press left
release left

Right click:
press mid
press right
release right
press right
release right
press right
release right

Middle click:
press right
release right
press mid
qt.qpa.cocoa.window: QNSView mouseDragged: Internal mouse button tracking invalid (missing Qt::LeftButton)
press right
release right
qt.qpa.cocoa.window: QNSView mouseDragged: Internal mouse button tracking invalid (missing Qt::LeftButton)
press right
release right
qt.qpa.cocoa.window: QNSView mouseDragged: Internal mouse button tracking invalid (missing Qt::LeftButton)
press right
release right
qt.qpa.cocoa.window: QNSView mouseDragged: Internal mouse button tracking invalid (missing Qt::LeftButton)
press right
release right
qt.qpa.cocoa.window: QNSView mouseDragged: Internal mouse button tracking invalid (missing Qt::LeftButton)
press right
release right
release mid