In this log the problem occurs twice. Neither button gets clicked().

"5.8.0 xcb" ()
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchBegin device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointPressed, 1 points: (TouchPoint(166 (394.05,242.548 0x0) TouchPointPressed press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.05,242.548) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=394.05,242.548, screenPos=394.05,242.548, MouseEventSynthesizedByQt)
QPushButton(0x8d37a08, name = "B") QMouseEvent(MouseButtonPress, LeftButton, localPos=88,143, screenPos=394.05,242.548, MouseEventSynthesizedByQt)
PRESSED "B"
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointPressed|TouchPointStationary, 2 points: (TouchPoint(166 (394.05,242.548 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.05,242.548) delta (0,0), TouchPoint(167 (200.536,239.741 0x0) TouchPointPressed press 1 vel QVector2D(0, 0) start (200.536,239.741) 
last (200.536,239.741) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(166 (394.44,243.483 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.05,242.548) delta (0.390137,0.935562), TouchPoint(167 (200.536,239.741 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start 
(200.536,239.741) last (200.536,239.741) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(166 (394.44,243.483 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.44,243.483) delta (0,0), TouchPoint(167 (200.927,240.209 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (200.536,239.741) last 
(200.536,239.741) delta (0.390137,0.467789)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(166 (394.44,243.483 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.44,243.483) delta (0,0), TouchPoint(167 (200.536,240.677 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (200.536,239.741) last 
(200.927,240.209) delta (-0.390137,0.467789)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(166 (394.83,245.822 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (394.05,242.548) last (394.44,243.483) delta (0.390152,2.33894), TouchPoint(167 (200.536,240.677 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start 
(200.536,239.741) last (200.536,240.677) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointStationary|TouchPointReleased, 2 points: (TouchPoint(166 (394.83,245.822 0x0) TouchPointReleased press 0 vel QVector2D(0, 0) start (394.05,242.548) last (394.83,245.822) delta (0,0), TouchPoint(167 (200.536,240.677 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start 
(200.536,239.741) last (200.536,240.677) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved, 1 points: (TouchPoint(167 (199.366,243.25 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (200.536,239.741) last (200.536,240.677) delta (-1.17046,2.57283)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchEnd device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointReleased, 1 points: (TouchPoint(167 (199.366,243.25 0x0) TouchPointReleased press 0 vel QVector2D(0, 0) start (200.536,239.741) last (199.366,243.25) delta (0,0)))

Irrelevant logs edited out here.

QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchBegin device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointPressed, 1 points: (TouchPoint(179 (417.069,228.982 0x0) TouchPointPressed press 1 vel QVector2D(0, 0) start (417.069,228.982) last (417.069,228.982) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=417.069,228.982, screenPos=417.069,228.982, MouseEventSynthesizedByQt)
QPushButton(0x8d37a08, name = "B") QMouseEvent(MouseButtonPress, LeftButton, localPos=111,129, screenPos=417.069,228.982, MouseEventSynthesizedByQt)
PRESSED "B"
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointPressed|TouchPointStationary, 2 points: (TouchPoint(180 (224.335,228.748 0x0) TouchPointPressed press 1 vel QVector2D(0, 0) start (224.335,228.748) last (224.335,228.748) delta (0,0), TouchPoint(179 (417.069,228.982 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start 
(417.069,228.982) last (417.069,228.982) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(180 (224.335,228.748 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (224.335,228.748) last (224.335,228.748) delta (0,0), TouchPoint(179 (417.459,229.45 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (417.069,228.982) 
last (417.069,228.982) delta (0.390137,0.467789)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved|TouchPointStationary, 2 points: (TouchPoint(180 (224.335,228.748 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (224.335,228.748) last (224.335,228.748) delta (0,0), TouchPoint(179 (417.459,230.853 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (417.069,228.982) 
last (417.459,229.45) delta (0,1.40337)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointStationary|TouchPointReleased, 2 points: (TouchPoint(180 (224.335,228.748 0x0) TouchPointStationary press 1 vel QVector2D(0, 0) start (224.335,228.748) last (224.335,228.748) delta (0,0), TouchPoint(179 (417.459,230.853 0x0) TouchPointReleased press 0 vel QVector2D(0, 0) start 
(417.069,228.982) last (417.459,230.853) delta (0,0)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchUpdate device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointMoved, 1 points: (TouchPoint(180 (224.726,229.684 0x0) TouchPointMoved press 1 vel QVector2D(0, 0) start (224.335,228.748) last (224.335,228.748) delta (0.390152,0.935577)))
QWidgetWindow(0x8d45438, name = "MainWindow") QTouchEvent(TouchEnd device: "eGalax Inc. eGalaxTouch EXC7200-72E1" states: TouchPointReleased, 1 points: (TouchPoint(180 (224.726,229.684 0x0) TouchPointReleased press 0 vel QVector2D(0, 0) start (224.335,228.748) last (224.726,229.684) delta (0,0)))