ComboBox border not visible in strip controls when navigated via keyboard

[Syareel-Sukeri]

.NET version

.NET 10.0.100-alpha.1.25058.38

Did it work in .NET Framework?

Yes

Did it work in any of the earlier releases of .NET Core or .NET 5+?

This issue cannot be reproduced in .NET 8.

Issue description

When a ComboBox is added to any strip control (MenuStrip, ToolStrip, StatusStrip, ContextMenuStrip), its border becomes invisible when focused using the Tab or Arrow keys.

Current behavior (.NET 9.0 and .NET 10.0)
The ComboBox receives focus, but its border is not visible when navigated via keyboard.

Border10.mp4

Expected behavior (.NET 8)
ComboBox should display a visible border when focused, even when navigated via keyboard.

Border8.mp4

Steps to reproduce

1. Create WinForms .NET Core app with MenuStrip.
2. Add a ComboBox directly to the MenuStrip or use it as a dropdown item.
3. Run the project
4. Use the Tab or Down Arrow key to navigate to the ComboBox.

[Tanya-Solyanik]

Please investigate the root cause and update this bug with it.

[ricardobossan]

I was unable to identify the faulty commit so far because I encountered build issues with commits from around August 2024.

Here is the build output for one such commit:

12774.ccd88e25778bdff0140def65964f294680f79518.build.output.txt

However, I have determined that in .NET 10, this issue was resolved in commit f5fef932773ba9d899d839f84996c30d816954de.

This commit reverted changes introduced in PRs #11529 and #11761, which suggests those PRs likely caused this issue.

[Tanya-Solyanik]

@ricardobossan - thank you!
If f5fef93 fixes this issue and #12590, I would service this commit to NET9. @merriemcgaw - what do you think?

[merriemcgaw]

@Tanya-Solyanik I agree, let's go ahead and service this.

[chaowendy]

Verified the issue with 9.0.0 + private dlls built from release/9.0 branch, the issue has been fixed as below screenshot：

border.mp4

[Zheng-Li01]

Verified with .NET SDK 9.0.3 test pass build, the issue has been fixed same as above test results.