[Regression][Mixed DPI] Classic Win32 Checkbox Rendering Regression After Windows 11 24H2/25H2 Update (Build 26200.8875+)


Hello,

After a recent Windows 11 update, standard checkboxes in classic Win32 applications
(those that do NOT enable Visual Styles and are DPI-unaware) render incorrectly under
mixed-DPI multi-monitor environments.

This is a regression: it does not occur on earlier builds, and disappears when the
update is uninstalled.

Impact: Production line-of-business desktop applications are affected, with multiple
end-user reports. The issue reproduces every time the affected window is opened.


1. SYMPTOM
In a classic Win32 application (Visual Styles / Common Controls v6 NOT enabled),
standard checkboxes render incorrectly in a mixed-DPI environment:
 - The checkbox box is offset from its correct position.
 - The check glyph is rendered at the wrong size and position.
 - The caption alignment is also incorrect.
Consistently reproducible in the same environment.


2. WHEN (build comparison)
 - Build 26200.8655 : OK (not reproduced)
 - Build 26200.8875 : Reproduced
 - Build 26200.8894 : Still reproduced (latest)
The regression appears to have been introduced between 26200.8655 and 26200.8875.
Candidate updates:
 - KB5095093 (Build 26200.8737)
 - KB5101650 (Build 26200.8875, 2026-07-14)


3. ENVIRONMENT
 - Windows 11 25H2 (Build 26200.x) - confirmed
 - Windows 11 24H2 (26100.x) - may also be affected (same servicing base)
 - Mixed-DPI multi-monitor, for example:
     Primary  : 1920 x 1080 @ 100%
     Secondary: 3840 x 2160 @ 300%


4. TRIGGERING CONDITION
The issue occurs only when the application window is displayed on a monitor whose
DPI scaling is HIGHER than the primary monitor.
 - Primary monitor      -> renders correctly
 - Higher-scale monitor  -> rendering is incorrect


5. STEPS TO REPRODUCE
 1) Install Windows 11 Build 26200.8875 or later.
 2) Configure two monitors with different scaling factors (e.g., 100% and 300%).
 3) Run a classic Win32 application that:
      - is DPI-unaware (no dpiAware manifest),
      - does NOT enable Visual Styles (no Microsoft.Windows.Common-Controls v6),
      - contains standard Win32 checkboxes.
      (For example, an application built with Delphi 2007.)
 4) Move the application window to the higher-scale (non-primary) monitor.

Result:
The checkbox box and check glyph are rendered at the wrong size and incorrect position.
A minimal reproduction sample can be provided upon request.


6. WHAT WE CONFIRMED
The issue does NOT occur under the following conditions:
 - All monitors use the same scaling (100%)
 - The problematic Windows update is uninstalled
 - The higher-scale monitor is set as the primary monitor (after reboot)
 - Visual Styles (Common Controls v6) are enabled

The following does NOT resolve the issue:
 - Compatibility > "Override high DPI scaling behavior"
     (Application / System / System (Enhanced)) - all three had no effect


7. ANALYSIS (hypothesis, not confirmed)
Without Visual Styles, classic checkboxes appear to be rendered through
DrawFrameControl(). This path does not participate in DPI virtualization and appears
to size the check glyph using the PRIMARY monitor's DPI. In a mixed-DPI environment
this makes the glyph and the checkbox frame misaligned on a higher-scale monitor.
A recent Windows update appears to have changed this rendering behavior, introducing
the regression.


8. REQUEST
Because uninstalling the update restores the expected behavior, we believe this is a
Windows update regression. Legacy Win32 desktop applications (including those built
with older toolchains such as Delphi 2007) are still widely used, and this issue
specifically affects applications that use classic common controls without Visual Styles.

After investigation, please consider one of the following:
 - Provide a Windows fix update.
 - Apply a Known Issue Rollback (KIR).
 - Publish an official workaround or guidance.

We are happy to provide a minimal reproduction sample, screenshots, logs, or any
additional information upon request.

Attachments:
 - Win11_CheckBox_Rendering_Expected.png
 - Win11_CheckBox_Rendering_Bug.png

Thank you.

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[한국어 요약]
최근 Windows 11 업데이트(Build 26200.8875 이상) 이후, Visual Styles(Common Controls v6)를
사용하지 않는 DPI 미대응 Classic Win32 애플리케이션에서 표준 체크박스가 혼합 DPI 멀티모니터
환경에서 잘못 렌더링됩니다(박스/체크표시/캡션 정렬 어긋남).

 - Build 26200.8655: 정상
 - Build 26200.8875 / 26200.8894: 문제 발생 (Regression)
 - 주 모니터보다 DPI 배율이 높은 모니터에서만 발생 (주 모니터는 정상)
 - 모든 모니터를 100% 배율로 통일하거나 업데이트를 제거하면 정상
 - 고배율 모니터를 주 모니터로 변경 후 재부팅하면 정상
 - Visual Styles(Common Controls v6)를 적용하면 정상
 - High DPI Override(Application/System/System Enhanced)는 효과 없음

업데이트 제거 시 정상 복구되는 점으로 보아 Windows 업데이트 회귀로 판단되며, 수정 업데이트
또는 Known Issue Rollback(KIR) 적용을 요청드립니다. 최소 재현 샘플/스크린샷/추가 자료 제공 가능합니다.