please provide the output of:
qdbus org.kde.KWin /KWin supportInformation

(In reply to Martin Flöser from comment #1)
> please provide the output of:
> qdbus org.kde.KWin /KWin supportInformation

Informations de gestion de KWin :
Les informations suivantes doivent être utilisées lorsqu'une demande d'aide est effectuée sur « http://forum.kde.org ».
Il s'agit de fournir des informations complémentaires sur l'instance actuellement lancée, les options utilisées, le pilote OpenGL et les effets actifs.
Veuillez poster le texte d'introduction ci-dessous grâce à un service de « copier / coller » tel que « http://paste.kde.org » au lieu de coller cela directement dans le fil de discussion de la demande d'aide.

==========================

Version
=======
KWin version: 5.14.4
Qt Version: 5.11.2
Qt compile version: 5.11.2
XCB compile version: 1.13

Operation Mode: X11 only

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: 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: 11906000
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.kwin.aurorae
Theme: __aurorae__svg__Adapta
Blur: 1
onAllDesktopsAvailable: false
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 9
decorationButtonsRight: 6, 3, 4, 5
borderSize: 3
gridUnit: 10
font: Noto Sans,10,-1,0,50,0,0,0,0,0,Regular
smallSpacing: 2
largeSpacing: 10

Platform
==========
Name: KWin::X11StandalonePlatform

Options
=======
focusPolicy: 0
nextFocusPrefersMouse: false
clickRaise: true
autoRaise: false
autoRaiseInterval: 0
delayFocusInterval: 0
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 4
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: false
electricBorderTiling: false
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: true
glStrictBindingFollowsDriver: true
glCoreProfile: false
glPreferBufferSwap: 101
glPlatformInterface: 1
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: DVI-0
Geometry: 0,0,1920x1080
Scale: 1
Refresh Rate: 59.9339


Compositing
===========
Compositing is active
Compositing Type: OpenGL
OpenGL vendor string: X.Org
OpenGL renderer string: AMD CAPE VERDE (DRM 2.50.0, 4.15.0-43-generic, LLVM 7.0.0)
OpenGL version string: 4.4 (Compatibility Profile) Mesa 18.2.2
OpenGL platform interface: GLX
OpenGL shading language version string: 4.40
Driver: Unknown
GPU class: Unknown
OpenGL version: 4.4
GLSL version: 4.40
Mesa version: 18.2.2
X server version: 1.19.6
Linux kernel version: 4.15
Direct rendering: Requires strict binding: yes
GLSL shaders:  yes
Texture NPOT support:  yes
Virtual Machine:  no
OpenGL 2 Shaders are used
Painting blocks for vertical retrace:  no

Loaded Effects:
---------------
zoom
kwin4_effect_fade
kwin4_effect_translucency
kwin4_effect_login
kwin4_effect_logout
kwin4_effect_maximize
kwin4_effect_windowaperture
kwin4_effect_morphingpopups
kwin4_effect_dialogparent
kwin4_effect_frozenapp
slidingpopups
slide
screenshot
minimizeanimation
desktopgrid
colorpicker
presentwindows
highlightwindow
blur
contrast
startupfeedback
screenedge
kscreen

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

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

kwin4_effect_fade:

kwin4_effect_translucency:

kwin4_effect_login:

kwin4_effect_logout:

kwin4_effect_maximize:

kwin4_effect_windowaperture:

kwin4_effect_morphingpopups:

kwin4_effect_dialogparent:

kwin4_effect_frozenapp:

slidingpopups:
slideInDuration: 150
slideOutDuration: 250

slide:
duration: 500
horizontalGap: 45
verticalGap: 20
slideDocks: false
slideBackground: true

screenshot:

minimizeanimation:

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

colorpicker:

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

highlightwindow:

blur:

contrast:

startupfeedback:
type: 1

screenedge:

kscreen:

Please enable electricBorderMaximize

(In reply to Martin Flöser from comment #3)
> Please enable electricBorderMaximize

It fixed it. Thank you.