Fixes #14020

Root Cause

The previous logic (Changed in #12205) allowed early returns or skipped updates under certain conditions (e.g., when regions were considered equal). This prevented PInvoke.SetWindowRgn() logic from executing, causing custom shapes like rounded corners to fail when the control handle was created or refreshed.

Proposed changes

• Remove conditional logic oldRegion == region from method SetRegionInternal of the Control class

Customer Impact

• Developers can display the expected shape after setting custom areas (such as ellipses or rounded corners) on controls such as buttons.

Regression?

• Yes

Risk

• Minimal

Screenshots

Sample project: RegionTest.zip

private void button1_Click(object sender, EventArgs e)
{
    var button = new Button()
    {
        Size = new Size(200, 200),
    };
    var path = new GraphicsPath();
    path.AddEllipse(0, 0, button.Width, button.Height);
    button.Region = new Region(path);
    this.Controls.Add(button);
}

Before

After

Test methodology

• Manually

Test environment(s)

• .net 10.0.0-rc.1.25553.112

Microsoft Reviewers: Open in CodeFlow