ToolStripTextBox cannot get focus in DemoConsole application

[LeafShi1]

Steps to reproduce

Test sample: DemoConsole in Winforms repo

1. Select ContextMenuStrip control.
2. Add a TextBox/ComboBox/Separator item
3. Select the new item

Current Behavior : ToolStripTextBox cannot get focus

Expected Behavior： All items can be focused normally

Notes: If add a extra ToolStrip control in the Tab page, everything will work well