When your mouse click breaks fullscreen and a clean Windows reset still doesn’t fix it

🚀 TL;DR

If you're playing Unity-based games (especially simulators) and every left-click causes a flicker or momentary loss of focus in borderless or fullscreen mode — and nothing seems to fix it — this guide documents:

  • The weird culprit: MSCTFIME UI (Windows IME engine)
  • All the failed fixes I tried (so you don’t have to)
  • The one solution that actually worked

🔥 The Symptom

  • Unity games (like simulation-style titles) would flicker whenever I clicked
  • Borderless fullscreen and even exclusive fullscreen were affected
  • OBS confirmed the flicker was in the rendered frame, not a display issue
  • Games ran at full FPS and smooth input otherwise
  • FocusLogger confirmed: MSCTFIME UI (via explorer.exe) stole focus every click

🔗 Diagnosing the Issue

Tools I used:

  • FocusLogger (by Jocys.com) to track window focus changes
  • Autoruns (Microsoft Sysinternals) to disable startup noise
  • PowerShell + Task Manager to find overlays and background services
  • OBS to verify if the flicker showed in captured frames
  • Heaven Benchmark to confirm non-Unity apps were unaffected

Confirmations:

  • MSCTFIME UI process from explorer.exe took focus on every left-click
  • The flicker was recorded in OBS — meaning it was software/render-based
  • Affected only Unity-based games, not Unreal, Source, or standalone engines
  • Fullscreen Heaven Benchmark had zero issues

❌ What Didn’t Work

Over several days of investigation, I tried literally everything:

Input-related fixes:

  • Changed language settings to single-language layout
  • Removed extra input languages
  • Disabled IME in every place possible
  • Killed ctfmon.exe and TextInputHost.exe
  • Disabled "Tablet Input Service"
  • Tried registry tweaks (ForegroundLockTimeout, LangBar, etc)

Display/driver fixes:

  • Full DDU wipe of NVIDIA drivers
  • Disabled overlays: Steam, Discord, Xbox Game Bar, GeForce Experience
  • Disabled fullscreen optimizations and forced DPI overrides
  • Tried different monitors and refresh rates
  • Swapped USB ports and mice

Background bloat:

  • Disabled Logitech, Razer, NZXT CAM, FxSound, OhMyPosh
  • Cleaned up startup entries using Autoruns
  • Disabled all non-Microsoft services via msconfig

OS resets:

  • "Reset This PC" with "Keep My Files" — did NOT fix it
  • Registry still had junk
  • IME services still active
  • MSCTFIME UI still showing in logs

🚮 What Finally Worked

“Sometimes the only fix is to wipe the slate.”

I did a true clean install of Windows:

  1. Downloaded the Windows 11 ISO directly from Microsoft
  2. Created a bootable USB using the Media Creation Tool
  3. Backed up everything manually
  4. Booted into the USB and deleted all partitions, including:
    • Windows boot
    • Recovery
    • System Reserved
  5. Installed Windows 11 clean from scratch
  6. Installed only:
    • GPU driver
    • Chipset driver
    • Windows updates
  7. Tested the game immediately before installing anything else

🌟 Result:

  • No more flicker
  • No MSCTFIME UI logs
  • Unity games worked normally in fullscreen and borderless

✅ Final Fix Summary (What You Should Do)

If you’re facing the same issue:

Backup:

  • Your Desktop, Documents, Downloads
  • Chrome profile (AppData\Local\Google\Chrome\User Data)
  • Anything else you might need to backup

Reinstall:

  1. Download Windows 11 ISO
  2. Create bootable USB
  3. Boot into installer
  4. Delete ALL partitions on the main drive
  5. Install fresh
  6. Install GPU/Chipset drivers only
  7. Run Windows Update
  8. Test your game BEFORE installing other apps

Optional (After confirming stability):

  • Reinstall apps one by one: NZXT CAM, Razer, Logitech, etc.
  • Stop at the first app that breaks focus again (if it does)

🤖 Who This Helps

This guide is for anyone who:

  • Clicks and sees flicker in fullscreen or borderless
  • Logs show MSCTFIME UI taking focus
  • Unity games minimize or lose focus on input
  • Tried everything short of nuking Windows

🚫 Lessons Learned

  • Reset This PC is not a clean install
  • IME bugs can survive resets and wreak havoc silently
  • Unity's input system is extremely sensitive to Windows overlay/focus bugs
  • The only guaranteed fix is: Delete partitions, clean install, test raw