SUMMARY
The Blur background effect applied to windows do not react correctly to other windows' content changes, leaving visible patches/rectangles that break the consistency of the blur effect. 

STEPS TO REPRODUCE
1. Open a window with a blurred background like Konole
2. Have another window below the aformentioned window update its content
3. Observe the blurred background not being repainted correctly
(see attachment)

OBSERVED RESULT
The window is only partially repainted, leaving a visible rectangle delimitation that breaks the blur effect's smoothness

EXPECTED RESULT
The background blur should be smooth and consistent across the whole window.

SOFTWARE/OS VERSIONS
Linux: 6.18.2-arch2-1
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
Wayland with PRIME setup

% lspci|grep VGA
00:02.0 VGA compatible controller: Intel Corporation Arrow Lake-S [Intel Graphics] (rev 06)
02:00.0 VGA compatible controller: NVIDIA Corporation GB203M / GN22 [GeForce RTX 5090 Max-Q / Mobile] (rev a1)
80:14.5 Non-VGA unclassified device: Intel Corporation Device 7f2f (rev 10)

% glxinfo | head -n15
name of display: :0
display: :0  screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
    GLX_ARB_context_flush_control, GLX_ARB_create_context, 
    GLX_ARB_create_context_no_error, GLX_ARB_create_context_profile, 
    GLX_ARB_create_context_robustness, GLX_ARB_fbconfig_float, 
    GLX_ARB_framebuffer_sRGB, GLX_ARB_multisample, 
    GLX_EXT_create_context_es2_profile, GLX_EXT_create_context_es_profile, 
    GLX_EXT_fbconfig_packed_float, GLX_EXT_framebuffer_sRGB, 
    GLX_EXT_get_drawable_type, GLX_EXT_libglvnd, GLX_EXT_no_config_context, 
    GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating, 
    GLX_MESA_copy_sub_buffer, GLX_OML_swap_method, GLX_SGIS_multisample, 

ADDITIONAL INFORMATION
All blur effects are affected, whether it be from the official Blur effect or 3rd party ones available e.g. on the ArchLinux AUR.