[BUG] Dark mode + DirectWrite rendering causes visual artifacts (line accumulation)

Is there an existing issue for this?

• I have searched the existing issues

Description of the Issue

Version: Notepad++ 8.8.7

Bug Description: When dark mode is enabled with DirectWrite rendering modes, yellow/orange lines (autocomplete hints) accumulate on screen and don't clear properly.

Steps to Reproduce:

1. Enable Dark Mode (Settings → Dark Mode)
2. Set rendering mode to "DirectWrite (default)" or "DirectWrite (DirectX 11)" (Settings → MISC.)
3. Restart Notepad++
4. Activate Notepad++ window
5. Leave window idle - lines gradually accumulate
6. Click in editor or lose focus - lines disappear immediately

Affected Rendering Modes:

• DirectWrite (default)
• DirectWrite (DirectX 11)

Working Rendering Modes:

• GDI (most compatible)
• DirectWrite (retain frames)
• DirectWrite (draw to GDI DC)

Workaround:
Change rendering mode to GDI to avoid the issue while keeping dark mode.

Steps To Reproduce

1. Enable Dark Mode (Settings → Dark Mode)
2. Set rendering mode to "DirectWrite (default)" or "DirectWrite (DirectX 11)" (Settings → MISC.)
3. Restart Notepad++
4. Activate Notepad++ window
5. Leave window idle - lines gradually accumulate
6. Click in editor or lose focus - lines disappear immediately

Current Behavior

Expected Behavior

Debug Information

Notepad++ v8.8.7   (64-bit)
Build time: Oct 19 2025 - 16:19:15
Scintilla/Lexilla included: 5.5.7/5.4.5
Boost Regex included: 1_85
Path: C:\Program Files\Notepad++\notepad++.exe
Command Line: 
Admin mode: OFF
Local Conf mode: OFF
Cloud Config: OFF
Periodic Backup: ON
Placeholders: OFF
Scintilla Rendering Mode: SC_TECHNOLOGY_DEFAULT (0)
Multi-instance Mode: monoInst
asNotepad: OFF
File Status Auto-Detection: cdEnabledNew (for current file/tab only)
Dark Mode: ON
Display Info:
    primary monitor: 1920x1080, scaling 100%
    visible monitors count: 2
    installed Display Class adapters: 
        0000: Description - Intel(R) UHD Graphics 770
        0000: DriverVersion - 31.0.101.5592
        0001: Description - Mirage Driver
        0001: DriverVersion - 2.0.105.0
        0002: Description - Microsoft Remote Display Adapter
        0002: DriverVersion - 10.0.26100.6725
        0004: Description - Microsoft Remote Display Adapter
        0004: DriverVersion - 10.0.26100.6725
    - warning, search has been limited to maximum number of adapter records: 4
OS Name: Windows 11 Pro (64-bit)
OS Version: 25H2
OS Build: 26200.7171
Current ANSI codepage: 65001
Plugins: 
    mimeTools (3.1)
    NppConverter (4.7)
    NppExport (0.4)

Anything else?

I think this bug hasn't been found yet, so I'm posting it to share.

No source file, test, or code entry point is identified. First reproduce the issue with Dark Mode and the two affected DirectWrite modes, compare them with the working rendering modes, and verify that autocomplete hint lines no longer accumulate while the window is idle.