.NET version

9.0.100-preview.7.24371.4 with dlls built from winforms repo of main branch. It cannot be reproduced with .NET SDK.

Did it work in .NET Framework?

No

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

Yes, this is a regression issue. Not reproduce on .NET 8.0

Issue description

When hovering over drop-down arrow of ToolStripComboBox, an additional blue hover effect appears outside the icon. This issue can only be reproduced with ToolStripComboBox which is in ContextMenuStrip, ToolStrip, MenuStrip. The issue cannot be reproduced with normal ComboBox.

Steps to reproduce

1. Create a WinForms .NET 9.0 project.
2. Add a ToolStrip component to the form.
3. Click the drop-down arrow on the ToolStrip to open the list of available items.
4. Choose ComboBox from the list to add it to the ToolStrip.
5. Build and run project.
6. Hover to drop-down arrow of the ToolStripComboBox and observe the result.