My wxFrame has a small thin 1 px border around it even though I asked for no border. Why?

Using开发者_如何学JAVA wxwidgets. I want a window without a border. I pass the follwoing flags to the frame wxFRAME_NO_TASKBAR | wxSTAY_ON_TOP but it still draws a black outline 1 px wide around the window. Is this a bug or something?

You must also set wxBORDER_NONE.