Windows Forms Application Icon suddenly shows as default icon or does not update color after KB5051989 update

Question

Hi,

Our C# Windows Forms Application icon (in the taskbar) suddenly shows as default icon or sometimes doesn't update its color (based on the customization) after installing the KB5051989 update. This has been working for 15 years, and the issue just appeared after the said update. Removing the update will make it work as usual. We have a VM that only have the KB5051979 update and there, the problem doesn't show up. The issue was also experienced by our clients, and we can also see this internally. Even after clearing the icon cache and rebuilding it, the problem still occurs.

There were a few cases, wherein I locked my machine while the application is running. And when I came back and logged in after a few minutes, the icon is displayed properly and with the correct color customization.

Here is a sample screenshot of the issue.

And here is the working one, without the update.

Here is the case where the taskbar icon did not update the color in the taskbar, but it is correctly shown in the Task Manager and in the live preview:

Is there something with K8SOS1989 update that may have affected taskbar icons of windows forms applications?

Any other advice that we can try to make it work as before?

Regards,

Emman G

Answer 1

Hi

This issue with taskbar icons not updating correctly after the Windows update (K8SOS1989) is interesting, especially since it worked flawlessly for 15 years before.

Based on your description, there appears to be a regression in how Windows handles application icons in the taskbar specifically after this update. The fact that it sometimes works correctly after a lock/unlock cycle suggests it might be related to the Windows Explorer shell's icon cache management or rendering.

Here are some potential solutions to try:

Icon Resource Loading: Review how your application loads and sets its taskbar icon. Ensure you're using the recommended APIs like SetWindowIcon or properly setting the icon in your application properties.

Handle Windows Messages: Implement explicit handling of system messages related to taskbar icon updates. Your application might need to respond to WM_TASKBARCREATED or similar messages to force icon updates.

Icon Format Optimization: Check if your icon resource formats might be affected by changes in the update. Try converting your icons to different formats or bit depths.

Application Manifest: Make sure your application has a proper manifest file that declares compatibility with the Windows version you're running.

DPI Awareness: Ensure your application correctly handles DPI scaling, as this can sometimes affect icon rendering.

Temporary Workaround: If feasible, you could implement code that periodically refreshes the application icon or forces a refresh when the application detects it's returning from a locked state.

Report to Microsoft: Since this appears to be a regression introduced by a specific update, consider reporting this to Microsoft through their feedback channels or support portal. Include your analysis showing it works with K8SOS1979 but not with K8SOS1989.

The fact that the icon appears correctly in Task Manager and live preview but not in the taskbar suggests this is likely a Windows shell rendering issue rather than a problem with your application's icon resources themselves.