Created attachment 105018 [details]
Screenshot of the issue

This has been happening for while. I can reproduce every time with my user account in a X11 session. I cannot reproduce with the same user in a Wayland session, neither with another user in a X11 session.

$ qdbus org.kde.KWin /KWin supportInformation

Version
=======
KWin version: 5.9.4
Qt Version: 5.8.0
Qt compile version: 5.8.0
XCB compile version: 1.12

Operation Mode: X11 only

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: yes
HAVE_INPUT: yes
HAVE_DRM: yes
HAVE_GBM: yes
HAVE_X11_XCB: yes
HAVE_EPOXY_GLX: yes
HAVE_WAYLAND_EGL: yes

X11
===
Vendor: The X.Org Foundation
Vendor Release: 11903000
Protocol Version/Revision: 11/0
SHAPE: yes; Version: 0x11
RANDR: yes; Version: 0x14
DAMAGE: yes; Version: 0x11
Composite: yes; Version: 0x4
RENDER: yes; Version: 0xb
XFIXES: yes; Version: 0x50
SYNC: yes; Version: 0x31
GLX: yes; Version: 0x0

Decoration
==========
Plugin: org.kde.breeze
Theme: 
Blur: 0
onAllDesktopsAvailable: true
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 1, 2
decorationButtonsRight: 6, 3, 4, 5
borderSize: 3
gridUnit: 10
font: Noto Sans,10,-1,5,50,0,0,0,0,0
smallSpacing: 2
largeSpacing: 10

Options
=======
focusPolicy: 0
nextFocusPrefersMouse: false
clickRaise: true
autoRaise: false
autoRaiseInterval: 0
delayFocusInterval: 0
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 3
focusPolicyIsReasonable: true
borderSnapZone: 10
windowSnapZone: 10
centerSnapZone: 0
snapOnlyWhenOverlapping: false
rollOverDesktops: true
focusStealingPreventionLevel: 1
legacyFullscreenSupport: false
operationTitlebarDblClick: 5000
operationMaxButtonLeftClick: 5000
operationMaxButtonMiddleClick: 5015
operationMaxButtonRightClick: 5014
commandActiveTitlebar1: 0
commandActiveTitlebar2: 30
commandActiveTitlebar3: 2
commandInactiveTitlebar1: 4
commandInactiveTitlebar2: 30
commandInactiveTitlebar3: 2
commandWindow1: 7
commandWindow2: 8
commandWindow3: 8
commandWindowWheel: 31
commandAll1: 10
commandAll2: 3
commandAll3: 14
keyCmdAllModKey: 16777251
showGeometryTip: false
condensedTitle: false
electricBorderMaximize: true
electricBorderTiling: true
electricBorderCornerRatio: 0.25
borderlessMaximizedWindows: false
killPingTimeout: 5000
hideUtilityWindowsForInactive: true
inactiveTabsSkipTaskbar: false
autogroupSimilarWindows: false
autogroupInForeground: true
compositingMode: 1
useCompositing: true
compositingInitialized: true
hiddenPreviews: 1
glSmoothScale: 2
xrenderSmoothScale: false
maxFpsInterval: 16666666
refreshRate: 0
vBlankTime: 6000000
glStrictBinding: false
glStrictBindingFollowsDriver: true
glCoreProfile: false
glPreferBufferSwap: 101
glPlatformInterface: 2
windowsBlockCompositing: true

Screen Edges
============
desktopSwitching: false
desktopSwitchingMovingClients: false
cursorPushBackDistance: 1x1
timeThreshold: 150
reActivateThreshold: 350
actionTopLeft: 0
actionTop: 0
actionTopRight: 0
actionRight: 0
actionBottomRight: 0
actionBottom: 0
actionBottomLeft: 0
actionLeft: 0

Screens
=======
Multi-Head: no
Active screen follows mouse:  no
Number of Screens: 1

Screen 0:
---------
Name: VGA-1
Geometry: 0,0,1920x1200
Refresh Rate: 60.0186


Compositing
===========
Compositing is active
Compositing Type: OpenGL
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile 
OpenGL version string: 3.0 Mesa 17.0.3
OpenGL platform interface: EGL
OpenGL shading language version string: 1.30
Driver: Intel
GPU class: SandyBridge
OpenGL version: 3.0
GLSL version: 1.30
Mesa version: 17.0.3
X server version: 1.19.3
Linux kernel version: 4.10.9
Direct rendering: Requires strict binding: no
GLSL shaders:  yes
Texture NPOT support:  yes
Virtual Machine:  no
OpenGL 2 Shaders are used
Painting blocks for vertical retrace:  no

Loaded Effects:
---------------
zoom
slidingpopups
kwin4_effect_login
slide
screenshot
kwin4_effect_windowaperture
minimizeanimation
kwin4_effect_translucency
desktopgrid
colorpicker
kwin4_effect_fade
kwin4_effect_morphingpopups
kwin4_effect_maximize
presentwindows
kwin4_effect_dialogparent
highlightwindow
blur
contrast
startupfeedback
screenedge
kscreen

Currently Active Effects:
-------------------------
kwin4_effect_fade
blur
contrast

Effect Settings:
----------------
zoom:
zoomFactor: 1.2
mousePointer: 0
mouseTracking: 0
enableFocusTracking: false
followFocus: true
focusDelay: 350
moveFactor: 20
targetZoom: 1

slidingpopups:
fadeInTime: 150
fadeOutTime: 250

kwin4_effect_login:

slide:

screenshot:

kwin4_effect_windowaperture:

minimizeanimation:

kwin4_effect_translucency:

desktopgrid:
zoomDuration: 300
border: 10
desktopNameAlignment: 0
layoutMode: 0
customLayoutRows: 2
usePresentWindows: true

colorpicker:

kwin4_effect_fade:

kwin4_effect_morphingpopups:

kwin4_effect_maximize:

presentwindows:
layoutMode: 0
showCaptions: true
showIcons: true
doNotCloseWindows: false
ignoreMinimized: false
accuracy: 20
fillGaps: true
fadeDuration: 150
showPanel: false
leftButtonWindow: 1
rightButtonWindow: 2
middleButtonWindow: 0
leftButtonDesktop: 2
middleButtonDesktop: 0
rightButtonDesktop: 0

kwin4_effect_dialogparent:

highlightwindow:

blur:
blurRadius: 12
cacheTexture: true

contrast:

startupfeedback:
type: 1

screenedge:

kscreen: